Thanks for this video. Brand new testing technique for me. My wife's car has this problem. 05 Corolla. No codes, and no obvious causation. Will have to see if any of my scan tools have this function. Thanks so much for the video, and your further explanations in the comments here. New subscriber here. Have been fixing vehicles for decades as an amateur, who also helps friends and neighbors. This last year, I am really investing in learning advanced diagnostics, as so much is computerized now. Make it a blessed day, for only you can. Thanks for your knowledge.
I have this exact issue with my 08 Sequoia. The pedal travel is excessive in my opinion. I have replaced the Master Cylinder twice and have completely done the brake system sans the controller and booster. My scan tool does not have this valve test function so I cannot run this exact test. However, my scan tool does measure the master cylinder stroke, and the stroke sensor appears to have a flat spot where it gets to a certain point, (a short distance from brake application) and it simply reads back the maximum stroke. Having replaced everything else I am down to the controller, and/or the booster (which contains the stroke sensor). The idea of buying new abs/vsc is off the table for $$$, am uneasy about used, for the reason that I buy one, install it and end up with the same problem and a days work down the toilet. Looking for some advice on how to proceed.
John, Thank you for posting this video. even being an engineer for years, we are still learning every day. Got a few questions for you Problem: I have the exact same truck and the same issue you have described. I used the software to test the ABS hold and release solenoids and applying brake pressure through the pedal, one of wheel behave differently from the rest whether triggering the "SFRR" or "SRRR", the pedal will travel further as you activate it, it only applies to the passenger rear, so it is obviously different when thing should be identical to each wheel, then I went on to study this particular ATE ABS hydraulic circuit online, but seem like I can’t find an exact match of what I am looking for, without the missing information, I can’t seem to connect the dot, I hope you can shred some light since you are pretty smart using the elimination method to identify the problem. Given - Fluid is incompressible, the system is free of air, MC is in working order. Assumption 1 - The Tundra MC Hydraulic circuit should be pair as follow - (Front Driver/Rear Passenger) ( Front Passenger/Rear Driver) For this MC configuration, we assume both plungers is in working order. If not, this ABS test may not be valid. Assumption 2 - we are working on 12 valves units, for each wheel, there should be 3 valves, one being Solenoid Feed(NO), Solenoid Return(NC) , not sure about the last solenoid, I assume it is isolation, but the most online source does not show it. That is still puzzling me what are the last valves for. Either way, 12 valves total. Assumption 3- two Low-Pressure Accumulators (LPA), one for each individual MC circuit. Logic 1 - The purpose of the Solenoid Return is to control the pressure relief into a lower pressure region correct? if so, the pedal should move as the displacement increase with a given amount of fluid ( went into LPA)? This test tells us RR is the prove this logic is true, and 2 scenarios can happen- 1.) LPA is filled with Fluid(Where the fluid went exactly? I thought it is a closed system? I don’t see a return line back to the brake fluid reservoir like other design) 2.) LPA is not filled 3 solenoids are stuck mechanically and one is working? Logic 2 - It can be the RR circuit one-way valve or the solenoid bypass, or the rest of the circuit has an issue except RR. Without knowing the purpose of the last solenoid, I can’t make that conclusion
This is going to be fun, I cover a lot of this in our ABS/Traction Control system classes. First the control solenoids (valves) Originally ABS only needed two valves for each hydraulic circuit that it controlled. One valve to isolate the wheel (or wheels) and one to dump pressure from the wheel(or wheels) if it was still locking up. The low pressure accumulator should not be filled with fluid under normal circumstances. Fluid get's dumped to the accumulator when a wheel is locking in order to release it and get it to start turning again increasing tire traction. Newer traction control systems and automatic braking systems had to add a third valve to allow a brake circuit to be pressurized without pedal application. That valve has now claimed the name of the isolation valve. The original isolation valve is now called an inlet valve. There are three channel systems and four channel systems. Confusion can occur during testing if your tool does not alert you to the possibility that you may have a three channel system when it appears to give you controls for a four channel system. Count the lines connecting the ABS controller to the rest of the vehicle. 5 lines, A Three Channel System: Two for the master cylinder input, One for each front wheel output, (total 2) One for both rear wheels. 6 Lines. A Four Channel System Two for the Master Cylinder Input One for each front wheel output (total 2) One for each rear wheel output (total 2) The four channel system could be an "X" design, but doesn't have to be. The Three channel system is not an "X" design. Now for the fun part. The brake system is only a closed system (for hydraulic purposes) when the ABS/Dynamic Proportioning Valve/Traction Control Systems are inactive. The moment they become active you will have different pressures in the different wheel circuits so by definition (pascals law) they cannot at that point in time be a closed system. See if that helps you with your conjectures.
@@thecardoc100 That makes complete sense now, that's where all the ASC DSC ELSD(control by braking, not BMW M stuff) about, learn another new thing! I do have a four-channel system where it controls each individual wheel. I ran the following test - ABS Solenoid (SFRR)- Pedal sink further as solenoid energized (SFRH)- Pedal movement minimal after activated (SFLR)- Pedal movement minimal after activated (SFLH)-Pedal movement minimal after activated (SRRR)-Pedal sink further as solenoid energized (SRRH)- Pedal movement minimal after activated (SRLH)-Pedal movement minimal after activated (SRLR)- Pedal movement minimal after activated With your clarification, I think it narrows down to two possibilities- Case 1 - Fluid got to go somewhere, as soon as (either SF or SR) solenoid RR open, the fluid went into LPA, which is normal and all others failed to open mechanically therefore pedal only travel minimally. Case 2- Check valve for the RR inlet valve stuck open, cause a fluid leak at the inlet solenoid activation. All other check valves working properly but still don't explain why the pedal only moves minimally as the solenoid energized. This is just my curiosity and wants to understand better how ABS works, either way, I bought the ABS unit for replacement. John, it is nice talking with you, and great to have you in the automotive community- I use the following link to understand the system John talks about, I hope this helps everyone else who wants to learn about ABS www.underhoodservice.com/abs-esc-hydraulic-control-unit-modulator-diagnostics/
@@carlosk2752 Case 1 - Fluid got to go somewhere, as soon as solenoid RR open, the fluid went into LPA, which is normal and all others failed to open mechanically therefore pedal only travel minimally. For clarification, let's imagine that you have a dump (release) valve leaking and fluid is going into an accumulator for one of the wheels. The pedal will be low with each wheel because of that fluid loss, but will go lower, up to the maximum volume of the accumulator as the non affected brake circuit dump valves are operated. The key point is you will feel the pedal drop with the brakes that don't have a leaking dump valve. The one that is leaking opening the valve has no change since it has already lost fluid to the accumulator. Case 2- Check valve for the RR inlet valve stuck open, cause a fluid leak at the inlet solenoid activation. All other check valves working properly but still don't explain why the pedal only moves minimally as the solenoid energized. If I am following this correctly are you suspecting that you have two failed valves (both the inlet and the dump) for the same wheel? (in this case the right rear?) I'm certainly not going to say that can't happen given what often causes failures inside the valve body assembly but that would be a weird one for sure. When an inlet valve is closed for the brake circuit that has the problem, (just like in the video) that should result in a higher pedal until the command is turned off.
@@thecardoc100 Once I got the ABS replaced, I will do a bench test to energize each solenoid, then I know if my theory makes sense, but I think case 1 is what is happening like how you describe it. LCA should only on be indepednce per wheel for this to make sense. otherwise the leaking solenoid would have filled up with the shared LCA. I agree with you on this one - The key point is you will feel the pedal drop with the brakes that don't have a leaking dump valve. The one that is leaking opening the valve has no change since it has already lost fluid to the accumulator.
John, As I replaced the ABS module with a "remanufactured" one (by seller), bled the brake with TS, Reset ABS, align yaw and steering angle, the pedal have gone worse, now the pedal can be depressed all the way to the floor when the engine is on, however when the Engine is off l, it is firm. . Long story short, would you happen to have a hydraulic diagram for this particular ABS ? are the Holding and Reduction valve normally open? or normally closed? I used the TS to test the holding and reduction valve to " on " position, the pedal moves minimally. ABS such as Audi BMW and Nissan Ate MK60 unit, those bleeding process actually using the ABS pump drive the fluid out of the circuit, while TOYOTA only cycle the pump then bleed it manually, there maybe something different about it.
KNOWLEDGEABLE John Gillespie Tutorial great video brilliant thank you so much for sharing with us what you know 👍Take care and have a great day John Gillespie From Nick Ayivor from London England UK 🇬🇧
Awesome video was sent over here by the Mario channel - I have the same issues with and Audi A6 2017. Changer the master and still have the same issues. I can drive around town and it seems fine but when I drive on a highway and take an exit - scary. I tried the two man pump technique. And it even acts weird then - the pedal gets really hard . When the bleeder is opened it goes to the floor , but barely any fluid goes into the bottle- the pedal stays then the pedal will stay hard when pumped until I start the engine- then to the floor. It was the same symptoms with the original master. It has progressively gotten worst over the year or so. Ever since I had a coolent leak that put my car into limp mode and when I changed my rotors and pads almost a year ago now. The abs module is right below the coolent reservoir and there seems to be green tarnish on the top brake lines. The dealership fixed that issue so I am not sure of the extent of the leak was. I am at a loss. I have watched many videos and non seem to work - and there isn’t any air coming out of the lines when I pressure bleed as well….help! Also I have an OBDELEVEN scan tool.
Hi John, great video! I came across your video looking for support on what I think is the cause of a problem on my Dad's 2009 Tacoma 2.7liter, he's experiencing problems with the brake pedal gradually dropping almost to the floor when he comes to a complete stop. With no ABS or any other warning lights on panel, I concluded it must be Master Brake Cylinder, went and bought a new one, installed and bled the system and everything was normal for a day or so, it started behaving the same way, vehicle comes to stop and pedal gradually starts dropping, I'm guessing that it's a mechanical ABS failure since no warning light is on, given the year of the vehicle and since I don't own a scan tool, I can't do this procedure. Hi from Puerto Rico!
With the engine not running, pump the pedal three or four times. Release the pedal for five seconds. Then push and hold the pedal with a moderate amount of force. Take note of how far the pedal moved and how hard you are pushing against it. Now without letting up on the brake pedal start the engine. Tell me what the pedal does when you do this.
Hmmm, I'm not sure on the questions. I have never done that test before but I would think if you activate the release solenoids the pedal should drop while activated.
That is correct, as you activate the dump solenoids you should feel a pedal response and the pedal will drop. Now exactly what you will feel is going to be different with regards to what is actually wrong with the vehicle you are working on and which wheel solenoid you are activating. As given away in the title this is a mechanical failure in the hydraulic controller, specifically a failed dump valve (release valve). One important note on this is that the dump valve operation is pulse width modulated so what happens when you operate one with a scan tool as compared to the mechanical failure of a valve will be different.
@@thecardoc100 I have used line locks on the brake hoses to isolate a low pedal fault but I never tried activating the different valves. I'd love to hear some more detail on how you determine if it's internal or external the the modulator assembly.
@@ssrbob I'm glad you asked Bob. Looks like there isn't as much interest in this as I was hoping, but maybe it will help someone someday. Let's pick this up where I stopped the video, we know that the problem is in the right front but we don't know what the problem actually is at this point so here is what we have to do. We can feel how far the pedal travels with no commands so once the pedal stops moving, (about three quarters travel) we need to command a dump valve open. In this case I would choose the left front and see how far the pedal moves. It isn't much but it is very obvious when you have your foot on the brake. You can do two or three more activations and the pedal keeps dropping each time. Now that you know what operating a dump valve does to the pedal, release the pedal for about five to ten seconds and then apply it again. Just like in the video we again go about three quarters of the way to the floor without assist. Now when we command the RF dump valve open we have two possibilities, if the pedal sinks each time then the problem is in the line or caliper because operating the valve creates an additional place for the fluid to fill. If the pedal does not sink, then the accumulator is already full of fluid and the failed dump valve is confirmed. I hope this helps someone.
I have a toyota tundra 2003. the breaks hold the pedal to the top and break the truck. I change the abs control, the rear shoes, the calipers but doesn't work. The still hold pedal high and break the truck. Can you help about that please?
I'm struggling to understand the symptom as you are describing it. It appears you might be telling us that the brake pedal has very little travel and is real hard to push. If that is correct, what happens if you: 1. With the engine off apply and release the brake pedal about four to five times. 2. Now step on the brake pedal and hold it with an average amount of force. 3. Without releasing the brake pedal, start the engine. Did the brake pedal move towards the floor when the engine vacuum applied assist with the brake booster?
We have our 2011 tundra V8 in the dealer for 3 weeks now with the same issue, they have changed the master cylinder twice and now they said it the abs module. Before they get more money out of us, what do you think we should do? I’m really to replace it
Just a note before we go real deep into this. It is possible to have a similar symptom, the low brake pedal and have it be caused by something other than what I demonstrated in the video. So, we should always approach this and any vehicle diagnostic event with an open mind when starting testing. When a shop is struggling to figure something out, they don't work on it every day. The tech will put some time into the job and then when the "easy and most common" cause fails now they have to do some research and try different ideas in the attempt to prove just what is really going on. For the technician this is the worst-case scenario because of how flat rate works and especially how techs get paid to do diagnostic testing. Over the last few weeks and in between other work which is necessary for the tech to earn a paycheck, the tech (or other techs trying to see if they can figure it out) would spend unpaid time with this because no-one wants to fail, and they all would love to be the hero and solve this and get your car back to you. Did the dealer service advisor say how they came about the diagnosis at this point that it is the ABS, just like the video? You rarely get to speak to the technicians because fat rate pay plan requires them to be working at or above 100% efficiency and anytime doing anything other than working on a car is lost time and lost income for them. At this point get back hold of the service writer and maybe ask for the service manager and work with them to get an explanation. Feel free to get them to watch my video and see if they will allow the technician to join the discussion. If the technician performed a similar routine to what I demonstrated, he/she will be able to tell you exactly which valve has failed in the ABS, just like I proved this was the right front brake circuit. At that point you can then decide to have it repaired or not. If the technician doesn't have solid proof because a routine like this has not been performed it might help them to know that I am not only a lifetime career technician that emphasizes electronics and computer controls, but I am also a continuing educational instructor for professional technicians and travel around the country teaching technicians how to do this and many more routines. They are more than welcome reaching out to me and I would gladly assist them should they desire.
I have an 07 Tundra, just changed the front pads, rotors and left caliper cause it had two holes in the rubber. Now I can't get the new caliper to bleed. every other wheel is fine. Do I need to replace the ABS pump actuator?
@@thecardoc100 I used the Autel to bleed the rear right then, manually bled right rear by pumping the brake a few times holding the brake, opened the bleeder then closed the bleeder and repeated until all the air was out then did the same procedure on the left rear then right front and got to the left front thats where I have the issue
No, no guessing required. Think of this as a logic puzzle, the answer can be figured out with the information provided. If you have a brake pad that is seized and flexing that will give you a low pedal. Closing that wheel's isolation valve would give you a higher pedal as demonstrated. Opening the dump valve for the affected wheel would see the pedal dropping further than just a single apply because you now have somewhere else for the fluid to that wheel to go instead of only flexing the brake pad.
@@thecardoc100 I probably dont understand what that valve really is doing and how the "plumbing" inside the ABS unit looks like. Is the valve ONLY blocking the canals from the master cylinder and then there is another actuator pressurizing the system when the emergency brake is doing its thing? Never looked into how this systems work as i never really had to. If its NOT a rusted pad and its NOT a flexing brakeline and NOT a piston in the caliper that returns more than it should then i guess the fluid moves somewhere inside the ABS module where it shouldnt move. As in leaking past that valve into the chamber on the "other side" of it where my imaginary actuator lives. So leaky valve inside the module (Again, i have no clue how it looks inside the module. Im just picturing it in my head)
@@stevejakobsen2765 Trying to visualize this like you are doing is a great start. Realizing that you aren't sure what exactly is going on inside the ABS unit in as much as how ABS works now requires some research and study. See if you can find that information somewhere, maybe even search for someone else's video on the subject and then come back and see if this makes sense.
@@thecardoc100 Alright. So to me it seems like fluid is leaking past the valve for that wheel inside the unit and past the pump and into its accumulator. So faulty valve. We are NOT talking about air trapped in the system here, right? That was ruled out earlier on as i understood you right in the video.
Looking at pictures of a "regular" system it looks like each wheel got two valves. One outlet and one inlet valve. So according to THAT picture you have a leaking outlet valve. So when you do that test you could probably see the fluidlevel go UP in the reservoir when that valve is de-energized as the fluid that is supposed to go to the piston goes back up instead.
Assuming you have this same exact issue before the parts cannon was fired, how do you determine if it's actually the master cylinder or the abs controller? What if it's both? How would one diagnose that correctly
This is where the logic portion of diagnostics come into play. We ask ourselves just those kinds of questions and see if we can figure out the answer. In many cases the answer is discovered by asking the right question about the question like this. If it was the master cylinder, that would cause a loss of pressure to the brakes. Operating the valves with no pressure in the brake system while the pedal is already at the floor would? The answer you should be coming up with is have no effect. If the problem was with the electronic portion of the controller instead of the hydraulic portion, the first thing that I would expect to see is a trouble code for that solenoid circuit such as circuit too high, too low or not plausible. It's also likely that the scan tool will be kicked out of the test. From there if I was trying to command the solenoids and I couldn't hear them clicking as demonstrated, I would connect my low amps probe around the power or ground circuit for the controller and try to measure the current that would flow when the bi-directional command is sent with the scan tool.
@@thecardoc100 Okay, that makes sense. So to recap a bad master cylinder would cause the pedal to sink continuously, but the abs controller would cause the pedal to sink like you showed in the video?
@@firstlast--- This is where the "learned feel" will come into play so this does need to be practiced, but essentially yes a master cylinder failing has it's own specific behavior. In most cases when the ,master cylinder is just starting to fail a light brake pedal application will see it leak worse than a heavy application of the brake pedal. So the pedal drops "faster" with minimal pressure. Once you can feel that difference with the car, use a heavy apply to the pedal to make it fall slower and then operate the solenoids as in the video. That will give you more of a positive reaction to the solenoid operation. Pay close attention to how far the pedal moves with the dump valve operation. Once you fill the accumulator, or the valve closes you will feel the speed of the brake pedal movement change.
@@thecardoc100 I capped the master cylinder with an old brake line that I hammered flat to seal it up, pedal was rock solid, meaning the problem is not in the master cylinder, right? So now on to the ABS unit. Thanks for posting the video!
Excessive pedal travel was the symptom. The problem is a stuck open dump valve in the ABS hydraulic portion of the controller for the right front wheel.
@@ElAlskid No. The way ABS works is when the system detects a wheel is locking up it first closes the inlet valve to that wheel so no more fluid goes to that brake circuit. If the wheel is still locking up it then pulses the dump valve allowing the fluid to flow into an accumulator reducing the pressure to that brake. That fluid is then pumped to a high pressure accumulator and can be used to reapply the brake. This whole cycle can repeat around fifteen times per second so the pedal doesn't drop during an ABS event. When the dump valve leaks like it was in this truck, the fluid just fills the accumulator allowing the pedal to drop and that brake doesn't apply until the accumulator is filled. The pump doesn't run and the solenoids don't operate because there wasn't a brake locking up.
It's not about what part to replace yet for any vehicle other than the one I presented in this video. This is about learning how to test and prove if a symptom that a given vehicle has is being caused by the ABS or not. Do you have a vehicle that has a problem? If so, what is it (year, make, model, engine, transmission) and what is it doing?
That one needed the hydraulic control unit replaced. But that isn't really the important part of the video. Before anyone replaces a part like that they need to test correctly and prove what the problem is.
Thanks for this video. Brand new testing technique for me. My wife's car has this problem. 05 Corolla. No codes, and no obvious causation. Will have to see if any of my scan tools have this function. Thanks so much for the video, and your further explanations in the comments here. New subscriber here. Have been fixing vehicles for decades as an amateur, who also helps friends and neighbors. This last year, I am really investing in learning advanced diagnostics, as so much is computerized now. Make it a blessed day, for only you can. Thanks for your knowledge.
God bless you 👍 🙏 thank you
Very KNOWLEDGEABLE
John Gillespie
From Nick Ayivor from London England UK 🇬🇧
I have this exact issue with my 08 Sequoia. The pedal travel is excessive in my opinion. I have replaced the Master Cylinder twice and have completely done the brake system sans the controller and booster. My scan tool does not have this valve test function so I cannot run this exact test. However, my scan tool does measure the master cylinder stroke, and the stroke sensor appears to have a flat spot where it gets to a certain point, (a short distance from brake application) and it simply reads back the maximum stroke. Having replaced everything else I am down to the controller, and/or the booster (which contains the stroke sensor). The idea of buying new abs/vsc is off the table for $$$, am uneasy about used, for the reason that I buy one, install it and end up with the same problem and a days work down the toilet. Looking for some advice on how to proceed.
John, Thank you for posting this video. even being an engineer for years, we are still learning every day.
Got a few questions for you
Problem: I have the exact same truck and the same issue you have described. I used the software to test the ABS hold and release solenoids and applying brake pressure through the pedal, one of wheel behave differently from the rest whether triggering the "SFRR" or "SRRR", the pedal will travel further as you activate it, it only applies to the passenger rear, so it is obviously different when thing should be identical to each wheel, then I went on to study this particular ATE ABS hydraulic circuit online, but seem like I can’t find an exact match of what I am looking for, without the missing information, I can’t seem to connect the dot, I hope you can shred some light since you are pretty smart using the elimination method to identify the problem.
Given - Fluid is incompressible, the system is free of air, MC is in working order.
Assumption 1 - The Tundra MC Hydraulic circuit should be pair as follow - (Front Driver/Rear Passenger) ( Front Passenger/Rear Driver)
For this MC configuration, we assume both plungers is in working order. If not, this ABS test may not be valid.
Assumption 2 - we are working on 12 valves units, for each wheel, there should be 3 valves, one being Solenoid Feed(NO), Solenoid Return(NC) , not sure about the last solenoid, I assume it is isolation, but the most online source does not show it. That is still puzzling me what are the last valves for. Either way, 12 valves total.
Assumption 3- two Low-Pressure Accumulators (LPA), one for each individual MC circuit.
Logic 1 - The purpose of the Solenoid Return is to control the pressure relief into a lower pressure region correct? if so, the pedal should move as the displacement increase with a given amount of fluid ( went into LPA)? This test tells us RR is the prove this logic is true, and 2 scenarios can happen-
1.) LPA is filled with Fluid(Where the fluid went exactly? I thought it is a closed system? I don’t see a return line back to the brake fluid reservoir like other design)
2.) LPA is not filled 3 solenoids are stuck mechanically and one is working?
Logic 2 - It can be the RR circuit one-way valve or the solenoid bypass, or the rest of the circuit has an issue except RR. Without knowing the purpose of the last solenoid, I can’t make that conclusion
This is going to be fun, I cover a lot of this in our ABS/Traction Control system classes. First the control solenoids (valves) Originally ABS only needed two valves for each hydraulic circuit that it controlled. One valve to isolate the wheel (or wheels) and one to dump pressure from the wheel(or wheels) if it was still locking up. The low pressure accumulator should not be filled with fluid under normal circumstances. Fluid get's dumped to the accumulator when a wheel is locking in order to release it and get it to start turning again increasing tire traction.
Newer traction control systems and automatic braking systems had to add a third valve to allow a brake circuit to be pressurized without pedal application. That valve has now claimed the name of the isolation valve. The original isolation valve is now called an inlet valve.
There are three channel systems and four channel systems. Confusion can occur during testing if your tool does not alert you to the possibility that you may have a three channel system when it appears to give you controls for a four channel system. Count the lines connecting the ABS controller to the rest of the vehicle.
5 lines, A Three Channel System:
Two for the master cylinder input,
One for each front wheel output, (total 2)
One for both rear wheels.
6 Lines. A Four Channel System
Two for the Master Cylinder Input
One for each front wheel output (total 2)
One for each rear wheel output (total 2)
The four channel system could be an "X" design, but doesn't have to be.
The Three channel system is not an "X" design.
Now for the fun part. The brake system is only a closed system (for hydraulic purposes) when the ABS/Dynamic Proportioning Valve/Traction Control Systems are inactive. The moment they become active you will have different pressures in the different wheel circuits so by definition (pascals law) they cannot at that point in time be a closed system.
See if that helps you with your conjectures.
@@thecardoc100 That makes complete sense now, that's where all the ASC DSC ELSD(control by braking, not BMW M stuff) about, learn another new thing!
I do have a four-channel system where it controls each individual wheel. I ran the following test -
ABS Solenoid (SFRR)- Pedal sink further as solenoid energized
(SFRH)- Pedal movement minimal after activated
(SFLR)- Pedal movement minimal after activated
(SFLH)-Pedal movement minimal after activated
(SRRR)-Pedal sink further as solenoid energized
(SRRH)- Pedal movement minimal after activated
(SRLH)-Pedal movement minimal after activated
(SRLR)- Pedal movement minimal after activated
With your clarification, I think it narrows down to two possibilities-
Case 1 - Fluid got to go somewhere, as soon as (either SF or SR) solenoid RR open, the fluid went into LPA, which is normal and all others failed to open mechanically therefore pedal only travel minimally.
Case 2- Check valve for the RR inlet valve stuck open, cause a fluid leak at the inlet solenoid activation. All other check valves working properly but still don't explain why the pedal only moves minimally as the solenoid energized.
This is just my curiosity and wants to understand better how ABS works, either way, I bought the ABS unit for replacement.
John, it is nice talking with you, and great to have you in the automotive community-
I use the following link to understand the system John talks about, I hope this helps everyone else who wants to learn about ABS
www.underhoodservice.com/abs-esc-hydraulic-control-unit-modulator-diagnostics/
@@carlosk2752 Case 1 - Fluid got to go somewhere, as soon as solenoid RR open, the fluid went into LPA, which is normal and all others failed to open mechanically therefore pedal only travel minimally.
For clarification, let's imagine that you have a dump (release) valve leaking and fluid is going into an accumulator for one of the wheels. The pedal will be low with each wheel because of that fluid loss, but will go lower, up to the maximum volume of the accumulator as the non affected brake circuit dump valves are operated. The key point is you will feel the pedal drop with the brakes that don't have a leaking dump valve. The one that is leaking opening the valve has no change since it has already lost fluid to the accumulator.
Case 2- Check valve for the RR inlet valve stuck open, cause a fluid leak at the inlet solenoid activation. All other check valves working properly but still don't explain why the pedal only moves minimally as the solenoid energized.
If I am following this correctly are you suspecting that you have two failed valves (both the inlet and the dump) for the same wheel? (in this case the right rear?) I'm certainly not going to say that can't happen given what often causes failures inside the valve body assembly but that would be a weird one for sure.
When an inlet valve is closed for the brake circuit that has the problem, (just like in the video) that should result in a higher pedal until the command is turned off.
@@thecardoc100 Once I got the ABS replaced, I will do a bench test to energize each solenoid, then I know if my theory makes sense, but I think case 1 is what is happening like how you describe it. LCA should only on be indepednce per wheel for this to make sense. otherwise the leaking solenoid would have filled up with the shared LCA.
I agree with you on this one - The key point is you will feel the pedal drop with the brakes that don't have a leaking dump valve. The one that is leaking opening the valve has no change since it has already lost fluid to the accumulator.
John,
As I replaced the ABS module with a "remanufactured" one (by seller), bled the brake with TS, Reset ABS, align yaw and steering angle, the pedal have gone worse, now the pedal can be depressed all the way to the floor when the engine is on, however when the Engine is off l, it is firm. . Long story short, would you happen to have a hydraulic diagram for this particular ABS ? are the Holding and Reduction valve normally open? or normally closed? I used the TS to test the holding and reduction valve to " on " position, the pedal moves minimally. ABS such as Audi BMW and Nissan Ate MK60 unit, those bleeding process actually using the ABS pump drive the fluid out of the circuit, while TOYOTA only cycle the pump then bleed it manually, there maybe something different about it.
KNOWLEDGEABLE John Gillespie
Tutorial great video brilliant thank you so much for sharing with us what you know 👍Take care and have a great day John Gillespie
From Nick Ayivor from London England UK 🇬🇧
Hello. I have the same problem with an 06 Toyota Tacoma, I have changed everything and the problem continues. Do I need to program the ABS module?
Awesome video was sent over here by the Mario channel - I have the same issues with and Audi A6 2017. Changer the master and still have the same issues. I can drive around town and it seems fine but when I drive on a highway and take an exit - scary. I tried the two man pump technique. And it even acts weird then - the pedal gets really hard . When the bleeder is opened it goes to the floor , but barely any fluid goes into the bottle- the pedal stays then the pedal will stay hard when pumped until I start the engine- then to the floor. It was the same symptoms with the original master. It has progressively gotten worst over the year or so. Ever since I had a coolent leak that put my car into limp mode and when I changed my rotors and pads almost a year ago now. The abs module is right below the coolent reservoir and there seems to be green tarnish on the top brake lines. The dealership fixed that issue so I am not sure of the extent of the leak was. I am at a loss. I have watched many videos and non seem to work - and there isn’t any air coming out of the lines when I pressure bleed as well….help! Also I have an OBDELEVEN scan tool.
Hi John, great video! I came across your video looking for support on what I think is the cause of a problem on my Dad's 2009 Tacoma 2.7liter, he's experiencing problems with the brake pedal gradually dropping almost to the floor when he comes to a complete stop. With no ABS or any other warning lights on panel, I concluded it must be Master Brake Cylinder, went and bought a new one, installed and bled the system and everything was normal for a day or so, it started behaving the same way, vehicle comes to stop and pedal gradually starts dropping, I'm guessing that it's a mechanical ABS failure since no warning light is on, given the year of the vehicle and since I don't own a scan tool, I can't do this procedure. Hi from Puerto Rico!
I have a 2005 Toyota tundra brake pedal is extremely hard to press. Braking distance is poor. I cannot figure out what is causing it.
With the engine not running, pump the pedal three or four times. Release the pedal for five seconds. Then push and hold the pedal with a moderate amount of force. Take note of how far the pedal moved and how hard you are pushing against it. Now without letting up on the brake pedal start the engine. Tell me what the pedal does when you do this.
Hmmm, I'm not sure on the questions. I have never done that test before but I would think if you activate the release solenoids the pedal should drop while activated.
That is correct, as you activate the dump solenoids you should feel a pedal response and the pedal will drop. Now exactly what you will feel is going to be different with regards to what is actually wrong with the vehicle you are working on and which wheel solenoid you are activating. As given away in the title this is a mechanical failure in the hydraulic controller, specifically a failed dump valve (release valve). One important note on this is that the dump valve operation is pulse width modulated so what happens when you operate one with a scan tool as compared to the mechanical failure of a valve will be different.
@@thecardoc100 I have used line locks on the brake hoses to isolate a low pedal fault but I never tried activating the different valves. I'd love to hear some more detail on how you determine if it's internal or external the the modulator assembly.
@@ssrbob I'm glad you asked Bob. Looks like there isn't as much interest in this as I was hoping, but maybe it will help someone someday. Let's pick this up where I stopped the video, we know that the problem is in the right front but we don't know what the problem actually is at this point so here is what we have to do. We can feel how far the pedal travels with no commands so once the pedal stops moving, (about three quarters travel) we need to command a dump valve open. In this case I would choose the left front and see how far the pedal moves. It isn't much but it is very obvious when you have your foot on the brake. You can do two or three more activations and the pedal keeps dropping each time. Now that you know what operating a dump valve does to the pedal, release the pedal for about five to ten seconds and then apply it again.
Just like in the video we again go about three quarters of the way to the floor without assist. Now when we command the RF dump valve open we have two possibilities, if the pedal sinks each time then the problem is in the line or caliper because operating the valve creates an additional place for the fluid to fill. If the pedal does not sink, then the accumulator is already full of fluid and the failed dump valve is confirmed.
I hope this helps someone.
@@thecardoc100 Thanks for the explanation, I'm going to have try some experimenting with this.
I have a toyota tundra 2003. the breaks hold the pedal to the top and break the truck. I change the abs control, the rear shoes, the calipers but doesn't work. The still hold pedal high and break the truck. Can you help about that please?
I'm struggling to understand the symptom as you are describing it. It appears you might be telling us that the brake pedal has very little travel and is real hard to push. If that is correct, what happens if you:
1. With the engine off apply and release the brake pedal about four to five times.
2. Now step on the brake pedal and hold it with an average amount of force.
3. Without releasing the brake pedal, start the engine.
Did the brake pedal move towards the floor when the engine vacuum applied assist with the brake booster?
We have our 2011 tundra V8 in the dealer for 3 weeks now with the same issue, they have changed the master cylinder twice and now they said it the abs module. Before they get more money out of us, what do you think we should do? I’m really to replace it
Just a note before we go real deep into this. It is possible to have a similar symptom, the low brake pedal and have it be caused by something other than what I demonstrated in the video. So, we should always approach this and any vehicle diagnostic event with an open mind when starting testing. When a shop is struggling to figure something out, they don't work on it every day. The tech will put some time into the job and then when the "easy and most common" cause fails now they have to do some research and try different ideas in the attempt to prove just what is really going on. For the technician this is the worst-case scenario because of how flat rate works and especially how techs get paid to do diagnostic testing. Over the last few weeks and in between other work which is necessary for the tech to earn a paycheck, the tech (or other techs trying to see if they can figure it out) would spend unpaid time with this because no-one wants to fail, and they all would love to be the hero and solve this and get your car back to you.
Did the dealer service advisor say how they came about the diagnosis at this point that it is the ABS, just like the video? You rarely get to speak to the technicians because fat rate pay plan requires them to be working at or above 100% efficiency and anytime doing anything other than working on a car is lost time and lost income for them.
At this point get back hold of the service writer and maybe ask for the service manager and work with them to get an explanation. Feel free to get them to watch my video and see if they will allow the technician to join the discussion. If the technician performed a similar routine to what I demonstrated, he/she will be able to tell you exactly which valve has failed in the ABS, just like I proved this was the right front brake circuit. At that point you can then decide to have it repaired or not. If the technician doesn't have solid proof because a routine like this has not been performed it might help them to know that I am not only a lifetime career technician that emphasizes electronics and computer controls, but I am also a continuing educational instructor for professional technicians and travel around the country teaching technicians how to do this and many more routines. They are more than welcome reaching out to me and I would gladly assist them should they desire.
I have an 07 Tundra, just changed the front pads, rotors and left caliper cause it had two holes in the rubber. Now I can't get the new caliper to bleed. every other wheel is fine. Do I need to replace the ABS pump actuator?
What do you mean by you cannot get it to bleed? Is there no fluid getting to the caliper at all? (break the hose connection loose)
@@thecardoc100 i did it had a slow stream that turned into a drip
I borrowed an Autel mx808 from my brother and tried to bleed the ABS I just took the hose off again after I tried to bleed it and it just drips
@@33bighands How exactly are you trying to bleed the brakes?
@@thecardoc100 I used the Autel to bleed the rear right then, manually bled right rear by pumping the brake a few times holding the brake, opened the bleeder then closed the bleeder and repeated until all the air was out then did the same procedure on the left rear then right front and got to the left front thats where I have the issue
what scan tool is that?
Guessing game?
I guess the pad rusted solid to the bracket and the extra travel is from flexing the pad until it touches the disk
No, no guessing required. Think of this as a logic puzzle, the answer can be figured out with the information provided. If you have a brake pad that is seized and flexing that will give you a low pedal. Closing that wheel's isolation valve would give you a higher pedal as demonstrated. Opening the dump valve for the affected wheel would see the pedal dropping further than just a single apply because you now have somewhere else for the fluid to that wheel to go instead of only flexing the brake pad.
@@thecardoc100 I probably dont understand what that valve really is doing and how the "plumbing" inside the ABS unit looks like.
Is the valve ONLY blocking the canals from the master cylinder and then there is another actuator pressurizing the system when the emergency brake is doing its thing?
Never looked into how this systems work as i never really had to.
If its NOT a rusted pad and its NOT a flexing brakeline and NOT a piston in the caliper that returns more than it should then i guess the fluid moves somewhere inside the ABS module where it shouldnt move. As in leaking past that valve into the chamber on the "other side" of it where my imaginary actuator lives. So leaky valve inside the module (Again, i have no clue how it looks inside the module. Im just picturing it in my head)
@@stevejakobsen2765 Trying to visualize this like you are doing is a great start. Realizing that you aren't sure what exactly is going on inside the ABS unit in as much as how ABS works now requires some research and study. See if you can find that information somewhere, maybe even search for someone else's video on the subject and then come back and see if this makes sense.
@@thecardoc100 Alright. So to me it seems like fluid is leaking past the valve for that wheel inside the unit and past the pump and into its accumulator. So faulty valve.
We are NOT talking about air trapped in the system here, right? That was ruled out earlier on as i understood you right in the video.
Looking at pictures of a "regular" system it looks like each wheel got two valves. One outlet and one inlet valve. So according to THAT picture you have a leaking outlet valve.
So when you do that test you could probably see the fluidlevel go UP in the reservoir when that valve is de-energized as the fluid that is supposed to go to the piston goes back up instead.
Assuming you have this same exact issue before the parts cannon was fired, how do you determine if it's actually the master cylinder or the abs controller? What if it's both? How would one diagnose that correctly
This is where the logic portion of diagnostics come into play. We ask ourselves just those kinds of questions and see if we can figure out the answer. In many cases the answer is discovered by asking the right question about the question like this. If it was the master cylinder, that would cause a loss of pressure to the brakes. Operating the valves with no pressure in the brake system while the pedal is already at the floor would? The answer you should be coming up with is have no effect. If the problem was with the electronic portion of the controller instead of the hydraulic portion, the first thing that I would expect to see is a trouble code for that solenoid circuit such as circuit too high, too low or not plausible. It's also likely that the scan tool will be kicked out of the test. From there if I was trying to command the solenoids and I couldn't hear them clicking as demonstrated, I would connect my low amps probe around the power or ground circuit for the controller and try to measure the current that would flow when the bi-directional command is sent with the scan tool.
@@thecardoc100 Okay, that makes sense. So to recap a bad master cylinder would cause the pedal to sink continuously, but the abs controller would cause the pedal to sink like you showed in the video?
@@firstlast--- This is where the "learned feel" will come into play so this does need to be practiced, but essentially yes a master cylinder failing has it's own specific behavior. In most cases when the ,master cylinder is just starting to fail a light brake pedal application will see it leak worse than a heavy application of the brake pedal. So the pedal drops "faster" with minimal pressure. Once you can feel that difference with the car, use a heavy apply to the pedal to make it fall slower and then operate the solenoids as in the video. That will give you more of a positive reaction to the solenoid operation. Pay close attention to how far the pedal moves with the dump valve operation. Once you fill the accumulator, or the valve closes you will feel the speed of the brake pedal movement change.
@@thecardoc100 I capped the master cylinder with an old brake line that I hammered flat to seal it up, pedal was rock solid, meaning the problem is not in the master cylinder, right? So now on to the ABS unit. Thanks for posting the video!
I am confused , what was the problem????
Excessive pedal travel was the symptom. The problem is a stuck open dump valve in the ABS hydraulic portion of the controller for the right front wheel.
@@thecardoc100 But wouldnt that only cause excessive pedal travel when the ABS was engaged
@@ElAlskid No. The way ABS works is when the system detects a wheel is locking up it first closes the inlet valve to that wheel so no more fluid goes to that brake circuit. If the wheel is still locking up it then pulses the dump valve allowing the fluid to flow into an accumulator reducing the pressure to that brake. That fluid is then pumped to a high pressure accumulator and can be used to reapply the brake. This whole cycle can repeat around fifteen times per second so the pedal doesn't drop during an ABS event. When the dump valve leaks like it was in this truck, the fluid just fills the accumulator allowing the pedal to drop and that brake doesn't apply until the accumulator is filled. The pump doesn't run and the solenoids don't operate because there wasn't a brake locking up.
@@thecardoc100 Oh . Ok I get you , thank you
What part do you replace? and where?
It's not about what part to replace yet for any vehicle other than the one I presented in this video. This is about learning how to test and prove if a symptom that a given vehicle has is being caused by the ABS or not. Do you have a vehicle that has a problem? If so, what is it (year, make, model, engine, transmission) and what is it doing?
John, what was the ultimate fix for this issue?
That one needed the hydraulic control unit replaced. But that isn't really the important part of the video. Before anyone replaces a part like that they need to test correctly and prove what the problem is.
@@thecardoc100 Agreed. How much did the part cost?
@@drew7257 I only did the diagnostics. The shop took care of the repair.
I always trust a man ...
that wears white new balances