TCU help - Diagnostics not even giving short pulses

[dynatos]

Details:
Car is a 1g awd talon tsi - It's been stuck in limp mode for a while now. I went to pull the codes from the TCU, except there aren't any codes. Not even the short pulses you are supposed to get.

Inside, 2 caps had leaked - one of which was a tantalum cap that looked exploded.. I replaced these caps but still no diagnostic information (or even short pulses saying everything is ok). Also, turning the car to on and running through the shifter it's apparent it's not even trying to accuate the solenoid..

Summary / Actual Question
So - Is there something i should check before the TCU? Is there something else i can check? Is there a way to test if the TCU is working outside of the car?

I'm just out of ideas, and while i'm awaiting response on my want-to-buy ad and reply to sellers i thought i'd probe for some more info...

The board has no cracks, all traces are ok and there was no other corrosion except for the leakage from the cap.. i just HOPE i'm missing something...

[mini zilo]

Check the fuse box on the inside of the car under the dash. Look for a fuse labeled (A/T). It is a 10 amp fuse, it probably blew.

[dynatos]

Originally Posted by mini zilo

Check the fuse box on the inside of the car under the dash. Look for a fuse labeled (A/T). It is a 10 amp fuse, it probably blew.

Unfortunately, it didn't (oh how i wish that was it!) It didn't look blown - i went ahead and pulled it out and tested it - it's good.

Edit: I probed one of the harnesses at the tcu for power and saw 12v..

Any other ideas?

[GDNF2ET]

What year is the car ? You could get a junkyard TCU out of a non-turbo, if it will plug up (two plug or three plug ) than it will work if the TCU is your only problem...The shift points will be off...I've used a two plug 1.8L TCU in my 93 AWD just to see if it would work..It did, but the shift points were way too early..Different ratios, fwd.... Let me know if the TCU # is MD750092 ..

[steve]

The TCU design isn't as forgiving as the ECU to the 47uf cap leaking. When the electrolyte eats through the sense trace the regulator starts pumping 12v on the 5v power rail which blows the CPU and other chips.

Measure the 5v rail and if it's 12v you'll need to find a good TCU.

[dynatos]

Fantastic information guys - One last question for the purpose of searching..

From what I can find, all late 89-early/mid 92 TCU's are 3 plug and late 92 to 94 are 2 plug connections. Is this true?

GDNF2ET - yes, it's a MD750092.

I also was sold this unit, as a 90 FWD tcu. But the two plug one's i've seen are together, not like this (see picture) where the two harnesses are spaced so far apart.. Is this right?



if this IS right, does that mean there is a 90 tcu, 91-early 92tcu and late 92-94 tcu.. all having FWD/AWD models?

[GDNF2ET]

A 90 is like a transitional car..The picture is un-like any tcu plug I've seen, so it would make sense if it was a 90..I can get my hands on a Md750092 if you need one..Just email me..You are correct that an early 92 (MD750092)is a three plug and a late 92 (MD754076) is a two plug..
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These are TCU part #s

MD738998 91-92 FWD, 1.8L
MD750092- 90-92 AWD
MD750093 91-92 FWD, w/turbo
MD750525 91-92 FWD, 2.0L, w/o turbo
MD754075 93-94 FWD, w/turbo
MD754076 93-94 AWD
MD754077 93 FWD, 1.8L
MD754079 93 FWD, 2.0L, w/o turbo
MD756600 95 FWD, w/turbo
MD756601 95 AWD
MD756916 94 FWD, 1.8L
MD756917 94 FWD, 2.0L, w/o turbo
MD759736 96 FWD, 2.0L, w/turbo
MD759737 96 AWD
MD762042 97-99 FWD, 2.0L, w/turbo
MD762043 97-99 AWD
MR483685 97-99 FWD, 2.0L, w/turbo
MR483686 97-99 AWD

[dynatos]

Thank you guys so much for your help. I posted a tech article summarizing all my findings.

If you have anything you think I should change/add please let me know!