jakeshredder

I have a 1989 jeep Cherokee 4.0 automatic transmission and the other night I was driving home and I stopped at the light then it just randomly took off in 4th so I had to manually shift it all the way home. And every time I put it in drive it goes straight to 4th gear. Park reverse 1st and 3rd options work fine, the key still goes in and out of ignition easy Idk if it's a neutral safety switch, a solenoid issue, or electrical of some sort idk? Any ideas will help thanks

IJM

Probably solenoids, but how's the fluid level. Any codes or CEL?

cruiser54

Probably not. 89 throws no codes.

First off, find the fuse for the Transmission Control Unit.

Photo attached.

IJM

Oops. I missed the '89 part and didn't realize it was OBD-I. That makes sense that the TCU signal isn't' getting to the trans since it'll be stuck in 4th with no signal.

jakeshredder

thanks cruiser, I was wondering were that fuse was located, I will check that fuse, if it's not then I will probably have to drop the pan to check the solenoids.

jakeshredder

Thanks cruiser! It was the TCU fuse, I'm glad it was the fuse and not the solenoid (:

Bustedback

But the question is what caused the fuse to blow? They don't wear out and blow over time.

jakeshredder

if it was a short then I'll probably have to run the wire to Any 12V switched source, if not a short then I'll have to look into the servo

Bustedback

Look at the blown fuse. If it looks like it exploded you probably have a short to ground. If it looks like it kind of burnt out you probably have a solenoid drawing a lot of amps.

cruiser54

They just blew. Put new one in and keep on trucking.

I don't know if they blew from the resistance in that connector along with the corrosion or what.