TCM issues on my '92
 

Approaching 200k on the odometer, it started going into "limp mode", first occasionally, then more and more often, until it was MOST of the time. Mechanic went through diagnostic steps until he got to "Substitute a known good TCM", which he didn't have. I bought a used TCM on ebay - worked for about 5 blocks, then back to "limp". Seller sent another TCM - worked for MONTHS!...hundreds of miles, city and highway. Then, SLOWLY started having problems. For a while, we could tell it was shifting properly by the fact that the D4 light was off (even when D4 was selected). I could leave home, drive a few miles, then suddenly the D4 would come on and the tranny would shift to 3rd gear. It might go back to normal in a few seconds..or it might be a few miles. The return trip home from work might be the other way around - start out in limp mode, then change to normal halfway home. For a few weeks, I tried to find a pattern, but it seemed quite random. Finally, though, it seems to have gotten stuck in limp mode.
I put the old TCM back in - OK for a couple of blocks, then limp mode.
**The weird thing is that, with the old one, I have to shift to 1st to get it to start off in low gear, but with the replacement, shifting into 2nd position gets it into the lower of the 2 gears that are available.
When it works, it works well. Any suggestions as to what I should do next? We need to sell the car...and it would be great if someone needed it for non-highway use only...but if another TCM might fix it, I guess I would give it a try.

What code is presented by TCM (D4 or sport light flashes)?

Note TCM and ECM are separate on your model.

good luck

I think I tried that and didn't get a code...and it seems to me that the mechanic that did the troubleshooting said he didn't get one either.

Maybe I should try it again now. I need to find the instructions again...months ago, I searched and finally found something with a picture, I think.

Sticky thread at the top of this Gen.Tech. forum, called "common DIY" or something like that. That contains a link to a thread on reading error codes.

I tried it again - nothing flashes, no code. ???

Key to "on", does the D4 and CEL come on for ~2 seconds and turn off?

I'll check this evening. Is this with or without the jumper wire hooked up?

Without the jumper wire, the lamps will come on for 2 seconds when you turn on the key. That's a bulb check; you need to know that the bulb isn't burned out.

With the jumper wire installed, the CEL will come on and stay on, if there's no codes stored.

OK, I'll check.
Well, I know the D4 light works, at least - it stays on when I drive with the currently installed TCM.