Expert: Roland Finston - 8/16/2011

Question
Roland:
This is a follow on, the continuing saga of the Chrysler 300m with codes P0700,  P0731, P0715, P0720.  Ended up taking it to the Chrysler dealer since none of your suggestions fixed it.  It has been in their shop for 9 days now.   After 3 days,  I was told it needed hard wiring to the turbine & output sensors.  Cost would be $400.  That fixed the speedometer and took away the P0720 code.  Car still goes into limp mode.  After 5 days, was told that their simulator was broken and they would have to get one from another dealer to continue the diagnostics. When I went in to the dealership, the mechanic had the pan dropped so he could have a look inside (not sure what he was looking for).  Yesterday (8days) was told the replacement simulator was also broken, so they had to get another.  Then I got a call saying the TCM would have to be replaced at a cost of $584.  I was told that a used TCM could not be used as they are VIN specific.
My question is, are the  TCM's really VIN specific?   And my second question is,  should I trust that they are following the technical service manual in diagnosing and fixing the problem?  If the TCM is bad, would not that throw a separate code indicating that?

Answer
Hi Steve,
I doubt the TCM is VIN-specific, rather the VIN has to be entered into it with a diagnostic readout box in order to match that of the PCM. The TCM is probably year and model specific, but it has memory and that is then programmed to take the VIN and the gear ratio of the specific transmission. So unless there is a code showing a TCM fault (0604 or 0605) I believe that replacement is unwarranted.
I would however be concerned about the 0731 because if that is persistent even after changing the sensors and the sensor codes indeed no longer occur (but that would assume the car has been driven post-sensor replacement and no such codes continue) then the causes are most likely internal problems with the trans that require opening it up (with a small possibility of an issue with the solenoid pack as the only other choice before doing the rebuild).
I don't know about how to assess their competency. I would be inclined to take it elsewhere if you have any other independent shop that knows these transmissions, at this point.
Roland