False Lean P0171: '00 Toyota 4Runner
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- Опубликовано: 18 сен 2015
- This Toyota 4-Runner is getting terrible fuel economy and blowing black smoke out of the tailpipe. However, the trouble code is P0171-System too Lean!
Let's figure out why this engine computer is so confused...
Check out this video by James Danner on a similar Toyota false-lean condition:
• O3 TOYOTA V6 SYSTEM LEAN
Also included: BONUS MATERIAL (special request by Eric O. of South Main Auto Repair)! 
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You're a mechanic I could trust. Wish more guys were as smart and skilled as you.
About to break the 1,000 subscriber mark! Congratulations Ivan!
This confirmed the problem I thought my car has. Thank you for posting Ivan
Thanks for this video Ivan. Like you I'm starting my own mobile diagnostic business and I already had a client with a 99 toyota tacoma with a false p0171. When doing the circuit integrity of the upstream o2 sensor I found the sensor ground broken. Also, I learn with Paul that when doing the integrity test on the sensor signal wire all I needed to do was to touch B+ with one hand and sensor wire with the other. Pretty cool if you ask me ;) nice work Ivan.
Cool! At what location was the sensor ground broken?
motoYam82 right at the back of the Connector to the sensor. The truck was treated by 2 other garages and saw some parts replacement.
Yes, your body (and a high impedance test light) limit the current through the sensor part of the HO2S - which protects the sensor from damage.
I've made the mistake of putting battery voltage (12V) to the signal side of the sensor. It takes just a few seconds to damage the sensor. At first they (GM at least) act OK, then eventually fail and set a code - low voltage IIRC.
Thanks for posting the test results Ivan, like you mention it is the same results I was finding all the way back to 98 so far. Just something we have to keep in mind when we are doing WOT test and looking for rich conditions. Man what the heck is is with multiple O2 failures lately. We did 2 on the Dakota, you just did 2 on the tee-yota and now I have that Chevy 3500 in there with both downstream smoked... must be the moon phase...
+South Main Auto Repair Plus the two upstreams on that Chev 2500HD and an upstream AFR on a Lexus V6 earlier this week haha
+motoYam82 On that Chevy is it a gas or Diesel?
6.0L gasser.
I have a 2002 tee-yota 4 runner and my maf readings are after I cleaned it is 0.4 lb before start up and 0.47 lb at idle please help the only code is po171 and sometimes it’s shuts off, I put a new gas cap on it car runs great no gas mileage problem but that freaking light won’t stay off??
first let me congratulate you on your videos, you're very good, my comment is based on the values of your diagnostic tool, vehicle 6-cylinder naturally aspirated range air flow ranges from 3.5 to 5.0 g / s, and your reading it is above 10.
Great video and grats on hitting over 1k subs!
So upstream has voltage signal and faulty heater circuit. Downstream heater circuit is fine but faulty voltage signal. Is it possible the failure of the upstream sensor fouled the downstream sensor from a super rich condition? Maybe if they caught this early enough they could have saved the downstream O2?
In my Holden Commodore which runs the 5.7 litre Chevrolet LS1 V8 engine,a P0171 code is being set when the engine goes into closed loop mode ever since the left hand side catalytic converter got smashed in.
That car doesn't run any downstream o2 sensors & the check engine display goes away once the engine is accelerated under load.
I think that it just needs a new catalytic converter, I'm going to replace the whole exhaust system anyway as it has been patched up but the catalyst inside the catalytic converter is damaged as it has been rattling.
Apparently anything less than a 200 cell per inch catalytic converter including no cat or a gutted out one with a standard tune will cause the LS1s ECU to throw a lean code.
That's why they say that if you fit 100 cell per inch cats onto an ls1 engines exhaust system, the ECU will throw a lean code therefore will need a tune done.
The 100 cell per inch cats are illegal in Australia anyway so I'm going to fit a set of 200 cell per inch 2.5 inch Genie cats & headers,the cat back system will be the same Redback twin 2.5 inch system that's currently welded onto the cats,me replacing the whole lot will make it just a bolt on system again & a lot easier to replace a cat back system in the future !
Great video !
Ivan
great job
At 0:19, is that a double clamps on coolant outlet hose? Asking because recently I had a coolant leak problem there.
grasias ivan por esas clases
A tip with those GM trucks with the open loop mystery. Many GM trucks have a WOT open loop (and thus also applies to power enrichment) delay of up to 60 seconds. In other words conditions have to be met for a specific period of time before OL/PE will enable @ WOT. Seems to be more in the specific calibrations rather than based on GVWR or model year as many 1500 and SUV's often have similar delay. I've tuned a lot of these trucks with aftermarket tuning software and the OL/PE delay counter table can be seen and adjusted accordingly. I normally remove the delay entirely so the OL and extra fueling comes in instantly @ WOT.
Feel free to pass it along to Eric O. too.
+BERPSU1 Great info, thanks!
Great video,
So is open loop the pcm is running the engine off of programmed parameters? And closed loop its using a variety of sensors to run the engine?
Yes, PCM/ECM uses a fuel/spark map based on calibration data collected for coolant temp, TPS, RMP, MAF/MAP, BARO. It will also do this when the HO2S input may not be accurate (like when a O2 sensor related DTC is logged).
Also, IIRC GM HD trucks may also go Open Loop at idle when there's not enough heat in the exhaust stream to keep the O2 sensor in it's necessary operating temp range..
Ivan,On a Ford F-150, which uses 4 standard O2 sensors, if one pair or both pairs were in the wrong positions, with the backs being in the front holes and the front sensors plugged into the back holes, would that typically result in an extremely rich condition?Thanks
+douglas lee Wouldn't think so, maybe a slow response code. Now if the left and right was switched, then that might be the result. ScannerDanner has a couple case studies on switched O2 sensors:
ruclips.net/video/0GOzJQzVuVQ/видео.html
What would cause this code in 3 different vehicles that only had one factor in common and that’s where they get their oil change from? I believe the kids doing the oil changes are not plugging sensors back in properly when done checking for service needs. Even the new car is doing it now. Please advise? Thank you
Find a new oil change place lol! Never seen a car where you have to unplug sensors to "check for service needs"...except maybe the air filter :)
Been watching your videos & how you perform your diagnosis. Where did you get your training. I've subscribed..thumbs up 👍...alerts. keep them coming💪💯💪💯🏄♂️🏄♂️
Yazmin
Venice Beach CA ⛱
confused on the testing of the lower O2 test. What was bad? Ohms too high? Signal too high?
Working on 2000 RX300 with P0171. Upstream has been changed. B1S1.
Signal stuck low.
motoYam82 can you clean the end of these sensors?
very good
I have a 97 Toyota 4 runner and wad running fine and a few days ago went out started it went to town shut it off and come back out and tryed too start it just cranked I had a half tank of gas pulled it home sit for couple days went out tryed it cranked right up drove it a half a day turned it off and now won't start again don't think it's fuel pump Need all the help I can get and no ck engine light on
Thanks
Ivan I think that if the MAF is reading 10 GPS at idle on a 3.4 L V6 that would be a problem NO? Pls help with this! I mean if the PCM sees 10 GPS at idle will it not add a great deal of fuel? Thanks Joe.
+Joseph Tucci Hey Joe! How much should it read? I'm not sure of the specs, but let's do a quick "back-of-the-envelope" calculation:
Given: 3.4L engine idling at 900rpm at sea level, ambient temp 25C.
So every crank revolution, we are taking in 3.4/2 = 1.7L of air (4-stroke engine).
1.7L/rev x 900rev/min = 1,530L/min
1,530L/min divide by 60sec/min = 25.5L/sec
At sea level one liter of air weighs 1.2grams (1.2g/L) (Google to the rescue!)
So we have 25.5L/sec x 1.2g/L = 30.6g/sec.
HOWEVER, at idle our intake manifold VACUUM is ~19inHg.
So the intake PRESSURE is 29inHg (=1atm) - 19inHg = 10inHg.
In atmospheres this is 10inHg / 29inHg = 0.34atm
So our airflow for this engine at idle should be approximately:
30.6g/sec x 0.34atm = 10.4 g/sec
So that MAF reading seems to be OK!
Joe Tucci 4 stroke eng = 3.4 L of air every other stroke or am I wrong on that?
+Joseph Tucci Hi Joe I read your questions to Ivan, what I see on the vehicles I check is a relation between the litres of an engine and the g/ps . For me I thought over 10 was too high , I would have guessed between 3&4 g/ps I'm glad Ivan responded , my guess is obviously off quite a bit. At least now if I ever see a Toyota like that I will not be alarmed at the data pid. Interesting.
A little insight into why the Chevy truck stays stoich at WOT from an EFI Calibrators perspective:
Gas mileage is of primary concern on trucks, more so than power. So the factory often tunes trucks to not go open loop at WOT until certain conditions are met. Typically, that means about 60 seconds after you go full throttle and pass 5,000 rpm, which basically means never.
It's typical of a car to go open loop at 75 to 100% throttle. GM is usually 100%. Once the car goes open loop, it no longer uses the O2 sensors to achieve lambda 1.00 (EQ ratio 1.00, 14.7:1 air/fuel ratio). Instead, it ignores the O2 sensors and runs a predetermined fuel curve, which varies depending on load/airflow and engine RPM. But essentially, you can expect to see about a 25% enrichment (EQ ratio 1.25, lambda .80, air fuel ratio 11.7:1).
Lambda = 1 / EQ ratio
EQ ratio = 1 / lambda
Air/fuel ratio = Stoichiometric ratio * EQ ratio
Air/fuel ratio = Stoichiometric ratio / lambda
Stoichiometric ratio = 14.68:1 for straight gasoline
Stoich ratio = 14.08:1 for E10 gasoline, if pcm is tuned for that.
Commanded EQ ratio on a warmed up engine at idle or part throttle is 1.00. As you go WOT, that should enrichen towards EQ ratio of 1.25 or so. But not on trucks.
A richer air/fuel ratio than Stoich builds more power. Stoich is a lean but stable air fuel ratio. Running richer also cools the pistons off more with fuel. This helps prevent knock, and allows more timing to be commanded than normal.
Trucks generally never go open lool, and never enrich past an EQ ratio of 1.00 (Stoich 14.7 x EQ ratio 1.00 = air fuel ratio of 14.7). This means the combustion chamber is lean and hot, and not able to tolerate much timing.
So on a stock truck tune, you can expect that they are not going open loop at WOT unless you floor it for over 60 seconds. Maybe even never... it varies with the tune. By remaining lean, the motor knocks easily so the factory hardly adds any WOT timing.
That's two strikes against power, in an attempt to maximize fuel mileage. This is why these large engine trucks seem so gutless. They're not gutless motors... they're gutless PCM calibrations.
A quick change to the factory tune using HP Tuners software, or any of the aftermarket programmers available will cause the truck to go rich as soon as you go WOT. This will GREATLY increase power and torque, at possibly the expense of some gas mileage. But that really depends on your right foot.
If you datalog EQ ratio, and you see 1.00, and the truck remains in closed loop, you will see the O2 sensors keep switching 0 to .9 volts. If the commanded EQ ratio is greater than 1.00, you will see the O2 sensors go pig rich.
Generally, stock cars delay WOT open loop a little. Stock trucks never go open loop. And sports cars will go open loop And enrich rather quickly to maximize torque. More fuel allows the use of more timing and increases power.
Trucks at WOT have miserably low timing values, because they aren't rich enough to allow for higher timing without going into knock. Hope this explains why you see nearly all trucks remain at EQ Ratio 1.00 AND closed loop at WOT.
Steve @ Drag Radial Performance
Correction:
Air/uel ratio = Stoichiometric ratio / EQ Ratio
Air/fuel ratio = Stoichiometric ratio * Lambda
Stoichiometric ratio is typically 14.68:1 for most cars until modern years, as E10 gas (10% ethanol) became the norm. We now see the factory tunes come with 14.08:1 Stoich ratios commonly. This basically adds about 4% more fuel than the old days to achieve the same result. In other words, the more ethanol content there is in your gasoline, the more fuel is required to do the same work, and the lower your gas mileage will be. Ethanol = Same amount of air as before, but more fuel required to achieve the same final mixture. You can thank your government and Ethanol lobbyists for that 4% reduction in gas mileage.
+Steve Hulett Thanks for that detailed explanation, Steve! Kind of surprising they are trying to maximize fuel econ on trucks, when it is abysmal to begin with haha! This Chevy gave me a real kick in the pants at WOT...wouldn't really call it gutless :)
+motoYam82, the engine size alone will produce decent acceleration, good enough to meet the OEM requirements. But if you felt the kick of a re-tuned engine versus an OEM tuned engine, you would cry at the waste of potential power. Ask any LS Chevy owner who has had their truck retuned.
From a technicians point of view, this is only important for understanding that you may not see the front O2s go rich at WOT on most trucks. Most cars do go rich, but there may be some delay time on non-sports cars before they go open loop and rich, once they've gone WOT.
FYI, it is possible to be open loop and still command 14.7:1 (EQ ratio 1.00). Open loop and being rich often do go together, but aren't necessarily require to. For example, a warm engine idling in closed loop will command EQ 1.00, and the O2s will sweep from 0 to 1v. But that same warm engine with the O2 sensor unplugged will switch over to open loop, and probably still command EQ 1.00. The only difference would be that the O2 sensor would not be sweeping, and theoretically should just hover right at 450 mv.
As engine load and throttle increase, you will usually see EQ ratio increase. How much enrichment is added is based on engine RPM and load/airflow.
+motoYam82 - Oh, and the OEMs focus a lot on truck gas mileage. To jump from 13 mpg to 14 mpg is a huge deal in actual fuel consumption. To go from 35 mpg to 40 mpg in a little car sounds nice, but is actually not such a huge deal. It's more of a math trick. Seems strange, but mathematically it's true. So a big focus is on trucks, even if it sounds like small gains. It's not the mpg that counts, it's the percentage of fuel usage. for example, what if a truck went from 1 mpg to 2... It would be a 50% increase in mileage and a 50% reduction in fuel usage, but only 1 mpg in difference.
In most other countries they calculate in liters per 100km (inverse of miles per gallon), which is a more honest scale. Americans just don't want the big V8 trucks to look too bad on paper lol! Open loop, closed loop...doesn't really matter for these hungry beasts.
Good job Ivan.
Good vid Ivan, I am not sure what Toyota logic is but on some Nissan models when the up stream o2 goes bad the down stream takes over fuel control. Did you ever find out if Toyota does the same? Good info to know when diagnosing a fuel trim issue.
+George Heri I would love to know, but obviously in this case when both sensors die, the computer goes nuts and floods the engine lol. Should have also recommended an oil change!
Sorry, I'm not familiar with Toyota A/F Meter. But,
I know when a GM O2 signal is low (ie: leak in exhaust, misfire, ...) the ECM's response is to add fuel because the O2 signal is 'telling' the ECM there's too much Oxygen from the leak or unburned O2 in the misfiring cylinder.
For GM, the MIL is flashed when a misfire is severe enough to damage the converter.
What is the problem?
which Part of pa you from? I have a dodge neon with a p0171 problem I need figured out before the weekend. I wanted to get Danner to do it but I have no way to get ahold of him. You can pm me if you would. Thanks.
State College, PA
motoYam82 thats about an hour 40 from me. i am 2 hrs exactly sw of bellefonte.
I'm actually 15 mins west of downtown...40 mins from Altoona
My 97 Tacoma 2.7l is high idle when it's cold outside even when engine is up to temp.. I have replaced iac valve, temp sensor, cleaned throttle body and no vacuum leaks.. Only thing else I haven't changed yet is tps
what is the idle rpm? What is coolant temp fully warmed up?
+motoYam82 I don't have rpm gauge on my truck but it sounds like 1500-2000 and temp gauge reads a little below half after further researching does coolant run through iac valve?
does the rpm drop at all during warmup? Yes, the throttle body does have coolant running through it to open up an extra air passage for cold starts.
+motoYam82 idle does not drop at all in winter time and summer time it runs like a champ
+motoYam82 thanks for responding it was a simple swapping of some coolant hoses and now everything works great thanks..
That MAF is reporting high. Need to go back to the OEM with a nice cleaning.
That's very crazy
13:44 “…and that was the end of Ivan.”
Ivan your a pretty sharp guy. Man you hit the big time getting a video request from NY. Ivan do allow PM's to your channel I have a request as well , like I'm not a mover and shaker but would it be ok if I PM you ?
+Steve Rob Is it on a Chevy truck? This channel might start to lose subscribers if I post one more Chevy truck video LOL
No Chevys better ck your PM it's AM here up in muskrat dam so just a minute.
+motoYam82 It's a worldwide pattern failure, get used to it. :P
A tee-ota is a tie-otie in the south ;)
+Steve Allen At SMA they are Toy-oaters
+South Main Auto Repair They are also called te-oters down here in the south ;)
👍 👍
Is it a teaota or a toyota?
I would like to comment, in this case the problem lies in the flow meter reading is very high, I hope you take into account my comment.
+Renan Maradiaga What is your evidence?
you r cool
Black smoke is 4 Runner 2001
👍
Well one had to break eventually! Toyota A/F sensors are not the best on the earlier models. He's a lucky guy if his CATs survived. Nice video.
+Toyota Tech I think the cat internals get coated with carbon in extreme rich scenarios like this. Maybe time for Scotty K's lacquer thinner treatment?
+motoYam82 Nah Ivan ,,I think ETCG proved that only works on a new converter :)
+motoYam82
I really don't get that guy! How has he got so many subscribers? I'm gonna wheel spin home tonight.
+Toyota Tech he loves toyota's, it's all toyota love. ;)
dont you worry about cooking that computer by giving 12v at the ground wire Ivan?
+armando nika Nope! 200mA through the test light won't cook anything. That's the beauty of the test light compared to an ohm meter: a small load that checks wiring integrity but is safe on any circuit :)
+motoYam82 ok thank you :)
Give her the beans! Lol
In youtube video editor, click 'stabalize', then save.
Shtoo ta koya?
Aquí
teach me
help help help I had a lean in bank one condition I've changed my idle air control Upstream O2 sensor downstream O2 sensor all of my fuel injectors and now my fuel pump my spark plugs my wires in my coils now my truck is barely running you replied to my comments before on the O2 sensors my truck has a 3.4 liter 99 Toyota 4Runner Limited I'm at my wit's end thank you so much
mass airflow sensor was bad!!!!!!! on the computer it showed a range from 6 grams per second to 36 per second it was still bad..... why can't I find the data to tell me if that was too low......... now with a new fuel pump new injectors new O2 sensors no catalytic converter truck spins the tires from standing stop
wow that's a lot of parts...
Thank you I'm off roading with that right now it's got so much power it's crazy
what about the pcv valve?
Wow thats a lot of money for throwing parts at it.
waste of my time
That was clean in 2016 wow