I purchased an '03 GMC Savana 3500 from auction for the 6.0l/4l80e to swap into a '70 GMC. Vehicle had no driveshaft so I couldn't test drive. Fixed that and find the only gears I have are 2nd and reverse, which research says is "LIMP" mode. I have power to the transmission, but I also have fluid in the main connector to the transmission. Fluid looks great, very clean and my cheap scanner picks up no tranny related codes. I would love to see this thing shift out once before pulling for the swap. TIA for any help.

 

Check speed sensors. And tps sensor. Check grounds.

 

I guess I should add that I have to start the vehicle by bypassing the starter relay. Everything powers up with the key on but it will not turn over.

 

Bad key switch? If so that could be an issue.

 

Does your scanner show shift solenoid state data?

Check the Fluid Pressure Switch states as well, If the PCM thinks it's in manual 2nd.....The truck will take off in 2nd.



Attachment 718161

 

Buy a new valve body and all electronics. Off ebay.

 

What makes you say that? The fluid in the connector?

 

It's the most popular answer. Don't bother with anything else, start throwing parts at it until either you're broke or it starts working.

 

I see you had no questions for people who gave solid technical advice.

 

I guess I don't know what I don't know. I am a parts swapper, I suck at troubleshooting.

 

Swapped ignition switch and no joy. Is there a way to see what gear the transmission neutral safety switch says the transmission is in without a dash cluster?

 

 

Any preferred sources? Any to avoid? TIA

 

 

Is that the same one in Jackson? If so I may just go visit my buddy who lives in Terry and check them out.