1998 Classic, 4.0. From day one of getting this truck willed to me by an acquaintance who had stripped it down with good intentions of doing a ground up restoration and gave up, the Check Engine Light has been on with code 0740. As far as I've become familiar with that code, it meant that the torque converter was not going into lock-out. I attempted to remedy it by putting a solenoid/screen/gasket kit in it, swapping out the fluid over repeated pan drains/fills, checking/cleaning all the grounds, ringing out the harness, checking for voltages, cleaning connectors from the transmission to the TCM, and verbally paying homage to the god of swearing. Four days ago I removed the TCM and found some rust on top of the steel case. I opened it up (3 screws) and took a look at the PC Board contained inside. I checked for moisture damage but it looked great; nothing to visually fault it for. All the traces and mounted components were clean, no overheating to be seen and all solder joints looked secure.

That night I located a used TCM for $36.00 on eBay and bought it. I put it in today and that resolved the problem. Note: At 60 mph with the old TCM I was taching just shy of 2200 rpm. Tonight I took a highway run and found it taching just under 2000 rpm. No CEL. No codes. Happy camper.

 

Good catch , when you say TCM do you have a PCM and a TCM 2 computers or just one .

 

I have the PCM in the doghouse on the inside of the left fender adjacent to the air cleaner box, and the TCM on the left side of the tunnel inside the truck just above the gas pedal. The previous owner told me he had replaced the PCM thinking it would correct a bad idle and stumbling condition. That turned out to be a combo of bad IAC and manifold O2 sensor.

 

Interesting. You're one of the rare cases where the trans computer was actually bad. 99% of the time, it's something else.

 

That's my take on it, from reading owner problems and fixes, but for the money ($36.00) I took a 50/50 chance of buying a good or bad TCM and the upside of it was the fix. The seller claimed it was out of a normal running wreck so, if nothing else, I'd have a spare if it didn't fix the problem. But, the second I started the truck I knew it was fixed. Just for grins I ran it up and down the highway again this morning and no issues.

There's a company that specializes in TCM/PCM repairs. It might offer me a price for the bad one I have that exceeds the amount I paid for the one I bought.