1994 Sonoma SLS 4.3

Asked by May 06, 2015 at 01:37 PM about the 1994 GMC Sonoma 2 Dr SLS Extended Cab SB

Question type: Maintenance & Repair

Ok guys and gals, please have pity... lol I am 53 yr old female... The vehicle is a 1994 GMC Sonoma SLS 4.3 Auto transmission.
1. The truck was running great until the heater core went bad.
2. I took the dash out etc... replaced the heater core.
3. Truck wouldn't start... checked fuses and all that sort of stuff all good.
4. Then checked cluster plug and it was kinda damaged. I fixed the wires on that. Truck then started great and ran great but wouldn't change gears on highway, speedo wasn't working.
5. So then ordered new cluster panel, as I thought I messed it up, but speedo still doesn't work....still wont change gears, NOW power windows don't work.
Everything worked great on the truck before all the crap was taken out to replace the heater core.
What could be the problem???? I am so sick to my stomach fooling around with this thing. The truck has no rust and is in excellent condition inside and out. Motor sounds great.... Yes have thought about the sensor located on/in transmission, but how could it be bad it everything worked before?
I need help.... please... lol

5 Answers


Sounds like you may have missed a ground connection when you put the dash back in.

3 people found this helpful.

Bless your little heart... You are the only one who has responded as of yet. Guess I should have put a younger age at the top for myself. ha ha I will try that asap and will let you know.


I told you this from experience, I replaced in a burned up harness in the dash of an S10 one time and I missed a ground wire, all kind of weird things were happening until I found that ground, then everything was back to normal.

3 people found this helpful.

Some times on older cars, you fix one issue and something completely unrelated fails. Coincidence.. When that happens you have to go to the source. Auto tramny not shifting check the input and out put shaft sensors if equipped. If you disconnected the battery during your heater core work, the PCM, powertrain control module, computer, may have to re-learn idling, driving, shifting. You may have something as simple as a poor connection on the PCM plug, specifically the sensors from the tranny. The ground suggestion is and excellent check. If you had to tear your dash down to that point its possible a ground wire was under a screw you removed, and re-assembly it got missed. Your local library may have the actual manuals that the dealer uses to fix those vehicles. Chassis and body, drive train etc. 2 phone book thick books. Maybe online there. My library had them until recent change to a Chiltons type. Not as good as the actual manuals. I bought mine when i bought my truck. Still have them. They look daunting but are not. Well laid out and the actual diagrams etc. For truck. I haven't looked to see if you solved your issue. But if this helps... Paul

Hey I got hey 94 GMC Sonoma automatic transmission and it's slipping I was wondering since my friend gave me a 94 GMC that's a manual can I swap the transmissions in those with each other

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