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Is my tcu blown? I need help, jeep is almost undrivable.

srmitchell

srmitchell

NAXJA Forum User
Location
Mckinleyville (Humboldt) CA
I posted this on the jeep forum also, I really could use some advice.

I have a 1-2 tranny switch installed. It runs power from the positive, to the tcu, or to the second solenoid when I want second gear. It doesn't work right anyway, but I just keep it so it runs like stock. No issues.

Anyway, on sunday night, one of the wires slipped off, and it shorted out. The jeep died, gauges died. It would crank but the fuel pump didn't work, and no fire.

I changed out the engine shutoff fuse, (#11) and it runs fine.

BUT, I put the switch back, and the tranny now acts as though the tcu is gone.

Drive- Revs, but doesn't move
3- Revs, doesn't move
1-2-Stays in 1st.


Did the tcu fry? Is there a fuse I haven't found? All others are ok.

I need help because it is really hard to drive, and I don't want to burn up the tranny.

Thanks!
 
srmitchell said:
Drive- Revs, but doesn't move
3- Revs, doesn't move
1-2-Stays in 1st.
Click to expand...

Little bitty 10A(I think) fuse in the block under the hood. Check the small fuses, there's one that is part of the TCU. Your description above describes that perfectly. When I did the silly switch mod years ago I did the same thing...twice...before we figured out what was going on. :) Essentially what you've done is killed the power to the TCU and you've got the trans in manual mode. DO NOT try to drive in 3 or OD, you'll overheat the tranny real quick.
 
I just checed all the fuses. Underhood, and kick panel.

I mean ALL of them, All good.

Is there a inline fuse I can't see?

This is driving me crazy.
 
srmitchell said:
I just checed all the fuses. Underhood, and kick panel.

I mean ALL of them, All good.

Is there a inline fuse I can't see?

This is driving me crazy.
Click to expand...

Just in the off chance...check the fuses with an electrical tester. I've had fuses go that 'looked' fine but were bad.

You might also check the wires you were dinking with and maybe try unplugging/plugging the harness in the TCU.
 
Will do. Everything else is fine though, is there one tranny specific fuse I am leaving out?

I just ditctched the switch, and put the wires back together. Same results.

I've got a friend with a xj, he might let me test my jeep with his tcu.
 
Don't know about later models but the Renix XJ has an 'in-line' transmission fuse near the tranny controller unit. The controller on my Jeep is under the dash on the passenger side.
 
Thats what Im looking for, but its a totally different set up.

Anymore input on another fuse?

I used a tester on every fuse in the heep, all good.
 
I know what's been bugging me...what year is this thing? :) *tip* When asking for tech help, make sure to let us know what we're working on. ;)
 
Sorry, I missed that entire post. :D

I don't see now where you got the trouble code checked out. I thought the later models had a speed sensor tied into the computer... Have you had this code read yet? I also thought this 1-2 switch thing couldn't be done on the late model XJs...

I've got nothing more for you until we hear more about the code, I guess.
 
Yea, I'll check it out.

I'll report back.

-Oh, and people told me you could, but it would throw a cel, and no, It doesn't work. :(
 
You should have power at two wires going to the TCU. One is always live, and the other switches with the ignition. I don't have my FSM handy to tell you colors or pins, but I do know on the older units they were the yellow and red wires.
 
Yea, they are the blue/white, and ....... I on't remember. haha.

All the connections are now good, but it just won't work.

Im going to check the code at autoshop tomorrow.
 
:thumbup: Another thought, check your wiring to the Throttle Position Sensor. If there was a melt down and a wire is broken/burnt in two then the TCU gets no signal telling it when to shift. No TPS signal and tranny no worky. Stays in groundhog.
 
I have the same problem sort of but my 99 just stopped shifting and has this error code on the odometer "no bus". Is there an inline fuse near the TCU. Is the TCM and TCU the same thing?
 
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