TCU fuse blowing
02-03-2009, 03:27 AM
#1
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Year: 1989
Model: Cherokee
Engine: 4.0L
TCU fuse blowing
89 CHEROKEE 4.0L AW4 Auto Trans 4 wheel drive (which has no trouble shifting in 4H/L) Been having a problem with it not shifting on its own (works fine If I manually shift it) I checked the inline TCU fuse and it was burnt. Replaced the fuse and everything looked to be good. Test drove it which it took off like it should while in Drive. Got down the road and went to take off again but it started off in 4th/overdrive. Checked fuse and it was blown again. So my question is Where does the fused wire go to / where should I be looking to try and find the short? Anyone have a wiring diagram that might help? Or any help at all to try and find this short. Thanks
02-03-2009, 07:55 AM
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Year: 1990XJ/1989MJ
Model: Comanche
Engine: 4.0L Renix
Sounds like a locked up servo and it (Tranny) is wanting to be in 2 gears at once. This will blow fuses to prevent a locked up tranny. I have a FSM that has a wiring diagram but that is not going to help you because it is as thick as a Bible.
02-03-2009, 09:21 AM
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Year: 1987
Model: Cherokee
Engine: 4.0 liter RENIX I-6, DIY Cold Air Intake, 2.5 FM Exhaust, 3 Core Radiator
It sounds to me like the wire you found this inline fuse in, is the power (12V) line that goes to pin C15 on yout TCU connector. If you lose or take away power from this pin the tranny will go into a full manual mode. Meaning it just goes straight to whatever gear you have the gshifter in. The good news for you is that for a temp fix until you find your short. You can cut this wire and run it to any (12V) switched source. Switched meaning it turns off with the ignition switch. You tranny will shift fine so long as you have power going to this wire.
02-03-2009, 09:50 AM
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Year: 1989
Model: Cherokee
Engine: 4.0L
Thanks guys for your input I really appreciate it. I sure hope it's not a servo though. Later today I will run a new switched on 12v power wire to see if it's a short or not. If it blows the fuse then I will atleast know to quit looking for a short and start looking into the servo. Thanks again guys and I'll update after I give it a try.
02-03-2009, 10:50 PM
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Year: 1989
Model: Cherokee
Engine: 4.0L
Ran a switched 12v (fused) wire to the TCU and it works perfectly. I'm going to continue using the new 12v lead until I am able to pin point where the short is. Thank you both for your help. It is appreciated very much.
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