a4ld lock-up clutch won't engage

[rhauf]

a while back my a4ld in my '93 stopped quit engaging the torque converter bypass clutch on the freeway. i noticed the 3 wire plug that goes into the transmission (which controls this function) had frayed and shorted wires.. so i fixed the wiring, but unfortunately it still won't lock in. i have checked all the fuses under the hood and under the dash, and none are blown. is there another fuse somewhere for this? or did i burn up the unit that controls this function, and if so where is it located?

 

[92exp4x4]

The control for this function is part of the PCM. The PCM controls the 3-4 shifting and the T.C. lock up. You may have fried the circut in the PCM that controls this. I would look at the solenoid in the tranny first though.

 

[rhauf]

damn.. i guess i'll be changing out the pcm then in that case.

i can pretty much rule out the transmission as a possibility, because this problem started with the old transmission, and i just let it go since it was due for a new trans anyway. but the new trans won't lock up either.

 

[MrShorty]

The solenoid circuit is a pretty basic DC circuit. Any number of sensors could be feeding bad information to the PCM, causing it to not "choose" to engage the TCC. If you must "guess" the PCM might be the most expensive part to guess at.

I'd start with some basic diagnostic steps: Pull codes from the computer to see if anything comes up that might hint at why the TCC isn't locking. Then go through the TCC solenoid circuit and make sure there isn't a break in the circuit somewhere. It's a pretty basic DC circuit, so it shouldn't be too difficult to test with a voltmeter and a wiring diagram.

 

[Marvial]

I have a similar issue too...any experts out there?

My daughter bought a 94 ex, which we have worked with and which is now in fairly good shape. However, the TC lockup is "vague", and not distinct. I also found an old ex, also a 94, and on mine the TC lockup was very distinct as soon as I reached 70-80 km/h (45-50)

Now, my lockup has become "soft", after using the truck for a year. Sometimes I get a solid lock, sometimes it is weak. It does not seem to be related to cold/warm transmission. I checked the ATF, and it was low, I filled less than a quart to get the level into the crosshatch.

So, we now have the same problem on both trucks. I will haywire a light to the TC control so we can see when the PCM tries to lock, and that that works, but what would be the cause of "weak" or nonexisting lockup? What items are involved, modulator??, governor?? oil level??

Except for this, shifting is fine on both trucks, and they pull strong on all gears, albeit some slip on 4-th as explained.

Regards

The smallest ex club in Sweden.

Gullik

 

[Marvial]

Update.......if this helps someone

The fix to my 94 ex was extremely simple, I just filled upthe ATF fluid level. I had to do this twice, and it is very hard to see correct level. After topping up, the problem did not go away immediately, it took some 50 miles driving until i noticed "weak" lockup, new check of level, and 50 more miles it is now better than ever, ditinct but smooth .

My suspicion is that air or "foam" got into the valve body, and therefore it took many miles to get the fluid properly distributed.

My daughters EX still suffers from "weak" lockup, we will try same procedure to see if it also is sensitive to fluid level.