94 PCM in a 95

(I'm cross-posting this with the Roadmaster forum to reach the broadest audience)

I believe the part numbers are the same for the PCMs themselves, just the programming is different. My question is "How different"?

My transmission self-destructed. Case was damaged, could not be rebuilt. The transmission shop replaced it with one out of a pickup truck. I'm now beginning to suspect the replacement is actually a 94, which does not have the PWM TCC solenoid. Mine is throwing a DTC 83 and won't lock up the TCC, which would be symptomatic of a 94 transmission in a 95.

I don't have tuning software to tweak individual settings, but I do have the Tech2 and TIS. I could use the serial number of a 94 wagon with the tow pack to trick it into flashing 94 programming into my 95 PCM, which I think would make the PCM treat the transmission as a 94, stop throwing the code and allow the TCC lockup.

My question is what other problems might crop up? My car never had the air pump disable, which is the only possibility that I can think of. Does anyone know of any other differences?

If it runs on gasoline, I can fix it.

Check this out about the trans, may give you some insight.
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This is the important part:
To put a ’94 4L60E into a ’95 car: Direct bolt-in. The PCM must be reprogrammed with ’94 transmission base code to avoid setting a silent code (Check Engine Light (CEL) does not illuminate, but code stored in memory). Trans will operate normally without reprogramming, but the silent code (code 83) will inhibit TCC lockup. Three potential fixes (any one will work); 1. reprogram PCM so it doesn't look for the PWM solenoid, 2. Add the wire into the harness or swap the '95-96 harness into the car ALONG WITH the internal transmission harness with the PWM solenoid connected but leave the solenoid in the pan, not installed in the valvebody as a '95-96 setup would have, or 3. wire up a manual TCC lock switch by which you can lock and unlock the converter yourself.

95BRMW wrote:

Check this out about the trans, may give you some insight.
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Yeah, I've seen that, thanks.

Quote :

2. Add the wire into the harness or swap the '95-96 harness into the car ALONG WITH the internal transmission harness with the PWM solenoid connected but leave the solenoid in the pan, not installed in the valvebody as a '95-96 setup would have,

I have a far simpler solution: wire in an appropriate sized resistor between the B+ and PWM solenoid wires. No need to change harnesses inside or outside the transmission. The PCM is just looking for a voltage drop and a resistor can provide that. Now, it would help to know the resistance of the solenoid, but a bit of experimentation would provide that info.

Quote :

or 3. wire up a manual TCC lock switch by which you can lock and unlock the converter yourself.

That one sounds like a recipe for transmission damage. What if you forget to unlock, or have to slam on the brakes, etc. etc. etc.

Anyway, looks like I won't have to worry about it. The solenoid is there. The Tech2 can over-ride the programmed action on the code 83 and when I use the Tech2 to command the solenoid to activate, the torque converter locks up just fine. I talked to the transmission guy who thinks it's a bad solenoid. I dropped it off tonight and he's going to change the solenoid and check all the wiring tomorrow.

You don't have the old trans by any chance do you?  I put a 94 trans in a 96 before, I took the harness and PWM solenoid out of the 96 and put it into the 94 trans, then zip tied the solenoid to the harness and left it sit in the pan.  Took care of the light and the shifts were fine. Slightly different year, but it may work for yours.

Transmission guy said the solenoid was bad, he changed it, and all works fine now.

Damned if I know how he verified that it all works fine now though -- he never cleared the DTC, and with DTC 83 set, it won't lock up the TCC.

However, I happened to have brought my scan tool with me when I picked the car up, cleared the code and verified everything is indeed working properly now. For now. This rebuild better last more than 39,000kms.