Hello everyone, having trnny problems, electrical I think. My truck is a 1998.5 24 valve auto, approx. 120,000 trans all original as far as I know. The converter is weak and altogether is due for rebuild, but the problem came on all of the sudden, therefore I think electrical. I am a diesel mechanic, but caterpillar is my strong point. I had to run errands around town after work but didn't notice problem until highway. My truck is in what I think is limp mode. Only have third gear, no lockup, no OD. I had an identical problem previously but that was due to a simple relay in the wrong place mistake, but the symtoms are identical to having the Trans relay unplugged. Of course I already checked that and it is clicking also tried different one, but no help. I limped home and cleaned my battery grounds, but no help. My main question is..... Is there a separate Trans controller/ecm or is it contrlled by the egine ecm that is behind the air fillter housing. Any grounds to specifically look for?, one that is specifically for the trans controller. Anyone know specifically know what happens to kick trans into limp mode. I really need to get it going but, the motorcylce weather is pretty good so I shall ride rain or shine! Sorry lengthy. I will get a hypertech from a friend tommorow to find my codes. Hope for the best. Thank you for any help.

 

I had the same problem a year and a half ago.

There is a trans relay in the Power Control fuse panel under the hood.

I contacted Dave Goerend of GB transmissions and after several days of patiently talking me through pressure test procedures and readings, had me wire a "cheater" jumper across it to confirm that my problem was in the valve body electronics before TiminVa changed it out for all new Goerend goodies.
AWESOME change in the way the truck feels and handles power.

 

When i got off earlier I made a jumper and found that when I jumper as if the relay was turned on The trans now has 1st 2nd 3rd and lockup but still no OD. When OD id locked out lock up hits at 30mph When OD is on lock hits at 45, but in 3rd. Trans will never shift into 4th. Take out jumper and install a good relay and I am back to 3rd only, as if in limp mode again. Sounding like valve body problem now.

 

Yup, Your valve body electronics have taken the big Dirt Nap just like mine did.

 

Got the truck hooked up and had 7 codes, but erased and only 2 came back. P0753-shift solenoid fault, and P1693 Manufactureres control, Auxillary input auxilary output. I am wondering if I can just change the solenoid in question.