I'm trying to diagnose the underlying problem with a 2002
9-
5 2.0 automatic.
I have done a fair bit of research and previously diagnose that the TCM was faulty, changed that, did re adaption and everything appeared to be fine. Except it isn't after 50 miles or so it throws the error code again. It can be cleared when cold, it comes back when hot.
Now I know there is a theory that the problem is the SLT linear solenoid, and that may well be true, but I have done a fair bit of measuring and testing to be able to be sure of the diagnosis before I remove the valve cover or open my wallet.
The error occurs with the correct TCM and also a 2003 TCM that is "known good"
Transmission fluid temperature sensor - Has the correct resistance / translation to degrees C
Wiring, continuity and light bulb tests done on the wiring to all 3 linear solenoids
Resistance tests on the linear solenoids show all three reading
5.8 ohms. This is just a little higher that the
5-
5.7 ohms I have seen quoted, but all three are the same
Now the important new information, at least from my perspective:
PWM confirmed at 300hz
Current draw - virtually zero , maybe 60 ma
Duty cycle on the SLT 55% at idle in P, dropping to 38% at 2000 rpm
Now reading around I have seen a theory that problems with the linear solenoids cause the TCM to go into "high current" mode. I am pretty convinced that this is a myth. Why ?, well these two graphs below give the answer (courtesy of Sonnax)
Before I go any further I am trying to be certain that this is a mechanical problem rather than electrical. I have read and been told that with the development of the valve body the design of the SLT was changed with the electrical connector moving from the top of the SLT to the bottom which was done apparently to reduce contamination.
You can also see from the graphs that low amperage gives high line pressure (the opposite of the prior hypothesis), and also that the duty cycle is above the expected range. It makes sense to me that higher duty cycle would give higher line pressure, but not necessarily current.
I'll admit I haven't got my head around how the different control pressures work inside the box to provide a smooth shift, but do get how those pressures are tweaked by adaption to take account of wear over time. I also now understand that the linear solenoids can be rebuilt and are mechanically adjustable.
Any further thought or suggestions for me. Key to my understanding is answering the chicken and egg question. Does the TCM adjust the amperage to achieve a target SLT pressure, or is it the duty cycle that is adjusted. What is really throwing me is the high duty cycle combined with low current.
I would like to have a better understanding of how the TCM and solenoids work together and how to properly diagnose this, any help or knowledge appreciated
https://www.sonnax.com/tech_resources/1 ... nformation