S4Per

For those who have been following my cries for help here, in VAG forum,PCNW, and other forums I just figured it out! (and will document here for others in the future)

Symptoms:
-Transmission goes into limp mode, driveable but seemingly only in one or two gears (3/4)
- ABS and traction control (ASR) lights go on (but NOT the flashing BRAKE light in instrument cluster)
- may or may not be able to get into TCM via Vag-com
- did not matter if sitting for some time, driving, hot or cold. completely intermittent

VAG results:
- fault codes in ECU: 18034 P1626 (Data bus: missing message from TCU)
- fault codes in ABS: 18034 P1626 (same as above)
- fault codes in Intrument: 01315: Transmission control module and/or 01311: Information Data Bus Intermittent or Faulty
- fault codes in TCM: none, ever.

Things I tried:
- cleaned up a whole bunch of wiring underneath driver's knee bolster - tug/pull to see if I can trigger code
- unplug ABS module - - code would still trigger
- pulled out TCM from under carpet, tugged/pulled wire harness from it to see if I could trigger fault - unsuccessful
- pulled out instrument cluster and did the same - same result
- inspected ECU, and TCM harness connectors for bent/loose pins, and the modules themselves for the same - - looked good.
- took off cover of TCM to see if there was any obvious damage in there. I have a Tip Chip, so cover was previously removed. When I first did this, I saw only one metal 'latch' was still attached to the cover (usually there are 4-6 on a stock TCM), latch was also completely loose and fell off when I removed cover. No big deal - just the cover, and tape held the rest of it in place.

Well, well, well, little did I know that little piece would come back into the picture: sitting in the car 30 minutes ago, staring at the cluster after having been up until 3am last night doing any and all of the above for the 50th time, I turn the ignition on again, and as the TCM is still removed I put my right hand on it and move it back and forth (similar to, but apparently not exactly like I had done before). This time I moved it holding just the cover...and boom, rocking it back and forth would trigger, then clear the fault. Unbelievable. I try to see if it's the harness somehow by taping the cover down securely to the TCM and repeating: no fault this time. To prove again, I take off tape, and sure as ****:

If any one of the 3 sides of the TCM cover that usually touch the metal on the other half of the TCM case (the fourth touches the plastic wiring harness) IS NOT TOUCHING - the fault will happen. It basically shorts it out. That's it. Nothing more :|

I'm tired and ecstatic, happy to know I don't have to spend thousands of dollars by replacing modules or paying someone else to find this.

That is all.

-Per

fastdream

<golf clap> good job.

drgolfnut

good news. So I suppose the dyno is rescheduled?

S4Per

..hopefully still get in this week!

S4Per

thank you sir. let me tell ya', i almost lost my mind on this one!

slogotse

Hi im new to all this, have the same message but cant find the TCM UNIT can you help?

slogotse

18034 powertrain databus missing from TCU help

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Hi guys new to all this can any one help.
I have just got a 1.8t a4 b5 and it is wet inside on the passenger side footwell both in the front and back, the car is in limp mode and i can't find the TCM, no gears come up on then dash any hepl ?

P. Neims