Trans Control Module light - limp home mode

[JerryCede]

E36 93 318is. Trying a second time on this pesky issue. Periodically TCM light comes on - trans won't shift, stays in low gear. Shut engine down and restart usually clears the light and trans works OK. Sometimes takes 3 restarts.
Just serviced trans with high end synthetic ATF, but problem is still with me. Any ideas out there??

[medic754]

I am having the same problem with my 1994 325iC. Shutting off the car and waiting 30 seconds to restart it seems to temporarily fix the problem.

My understanding is that the fix is to replace the Transmission Control Module. I have found one at a junk yard for a reasonable price, but have no idea where it is on the vehicle.

I have Bentley's book and it doesn't show it. I have searched the web but cannot find any pics.

Anyone that can help me with locating this please email me at medic754@nycap.rr.com.

Thanks.

[JerryCede]

The short term fix I have found is turn the ignition on and wait for TCM light to go out before starting - seems to work.

[drgui]

I am having the same problem with the TCM light on my 1993 325is. If anyone knows where it is located and/or a fix, please post as it is driving me crazy. I've search my Chilton's Repair Manual and also the internet and cannot seem to find anyone with a fix to this pesky problem. Any leads is much appreciated. Thanks

[medic754]

It seems, after talking with a few people, that everyone's problems are just a bit different. Jerry's problem seemed to be related to water getting into the compartment where the TCM is located. My problem seemed to be simply that the computer was bad. Either way, if you are certain that there is no mechanical problem with your transmission, the fix is simple...replace the TCM.

I replaced mine this week and it is completely fixed. It is, however, a $1,000 part from BMW so you may want to search the junkyards first. I got mine for $100 and it works like a charm. The only catch with mine is that it came from a coupe instead of a vert and the shift points are slightly different. The vert's shift points in auto mode and shifter in "D" seemed a little more aggressive, but it works well so I can't really complain. I use it more in "sport mode" anyway.

I don't have the name and number of the place handy that I got my TCM from, but if you email me at medic754@nycap.rr.com, I'll get it to you when I get home. Maybe they have one that will fit your car.

As for the location of the TCM... it is in a small "cubby hole" inside the engine compartment directly behind the glove box. Standing in front of the car looking up toward the passenger compartment with the hood up, you'll see a foam cover with black plastic snaps holding it in place. Remove those clips by pulling them straight out. The foam will fold down out of the way. The plastic housing behind it can be removed by removing the four screws holding it in place. Inside the compartment you'll see two computers with large wiring brackets on them. Technically speaking, you should disconnect the ground wire from the battery before proceeding; your call. You'll need to remove the wiring brackets by lifting the silver levers up and then pulling the wires away. The bottom computer is the DME. It needs to come out first. Simply loosen the brass screws on each side of it and slide it straight out. You do not need to completely remove the screws. After the DME is out of the way you can remove the TCM by "popping" the front of it down toward the ground. Don't be shy, you may need to "force" it. After it pops down you can slide it out at an angle. To swap it for a new one you'll need to take the old one off the bracket that is attached to it and put it on the new one (assuming, of course the new one doesn't have one already on it). Installation is reversed.

I hope this helps. It seems like a lot of steps, but it is actually very easy. It literally took me 10 minutes to swap it out.

Good luck.