burning up tcus?

[92awdgsx]

hey guys, i hope someone can help me. i'm working on a 91 talon tsi. it was brought to me in limp mode. i tried pulling codes but didn't have any luck. the needle on the analog volt meter wasn't making the normal sweeps. it would make a couple little erratic movments, then it would make some bigger movements, and then it just stayed strait up and down, then it did nothing. and stayed doing nothing. so i put a tcu in that i had laying around that i knew worked. took it out for a test drive, i shifted fine for the first couple shifts. then i was slowing down and it down shifted into 3rd and that is were it stayed. it was in limp mode. i tested that one and it did the same thing. i tested my car to see if i was doing it wrong and i got the normals sweeps that you are suppost to get when there is nothing wrong. something is causing the tcu to go out and i don't know what it is. i ruined my extra one trying to get the talon to work and now i'm mad. i even unhooked it and let it sit over night and tryed pulling codes again and it did the same thing. would shorted out shift selinoids blow out the tcu? please someone help.

 

[transdude]

hey guys, i hope someone can help me. i'm working on a 91 talon tsi. it was brought to me in limp mode. i tried pulling codes but didn't have any luck. the needle on the analog volt meter wasn't making the normal sweeps. it would make a couple little erratic movments, then it would make some bigger movements, and then it just stayed strait up and down, then it did nothing. and stayed doing nothing. so i put a tcu in that i had laying around that i knew worked. took it out for a test drive, i shifted fine for the first couple shifts. then i was slowing down and it down shifted into 3rd and that is were it stayed. it was in limp mode. i tested that one and it did the same thing. i tested my car to see if i was doing it wrong and i got the normals sweeps that you are suppost to get when there is nothing wrong. something is causing the tcu to go out and i don't know what it is. i ruined my extra one trying to get the talon to work and now i'm mad. i even unhooked it and let it sit over night and tryed pulling codes again and it did the same thing. would shorted out shift selinoids blow out the tcu? please someone help.

Try to get the TCU codes pulled with a scanner, flashing them out doesn't always work.

While it is certainly possible for a shorted solenoid to fry a computer, I think it is more likely that the TCU is seeing something that it doesn't like and commanding limp.

Is the trans in limp permanently or does it start in first if you shut it off and start it again?

-John

 

[92awdgsx]

its stuck in limp perminantly with both computers. i put both computers in my car to see if i could get them to work because my car is working perfectly, and the computers won't come out of limp even in my car. i replaced the caps because i found they were leaking, and that didn't help.

 

[transdude]

Hmm,

Maybe you do have a short to ground- check the wires for solenoid a, solenoid b, the damper clutch solenoid and the pressure control solenoid for continuity with ground. If any of them have very little resistance- that's your problem.

Be careful, the PCS only has about 3 ohms to begin with.

-John

 

[steve]

i replaced the caps because i found they were leaking, and that didn't help.

Just like with the ECU, if the caps have leaked there is usually collateral damage. Sometimes I have to use a magnifing glass to find the opens caused by the electrolyte etching the traces. Not to say that's what wrong trans but since the TCU doesn't work in your car either I'd bet there was some other damage. If I had a way of testing them I'd start fixing them too.

Steve