Customer states coolant issues, coolant leaking from tank, CEL, MIL: PART 1

Customer states coolant is leaking from expansion tank, he believes he may have a compression issues.
The engine was rebuilt approximately 1 year ago at a different shop. The cylinder head was replaced around 1 month ago.
We do have an active Check Engine Light ON. We also have an active Malfunction Indicating Light ON.
The current fault codes are SPN 84 FMI 4 Vehicle Speed Sensor Circuit Failed LOW

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Good video thank you Pedro. The Regen temps looked great so maybe short trips and/or long idling times could've plugged the doc. Nox readings looked good but beware of faulty def pumps on these models. I start to question them when they rotate 12-1300rpms. 950-1050 is ideal