Greetings Chevrolet forum members,

I have a 2003 Chevrolet Silverado that I have owned for 12 years. It is an LS extended cab, 2WD and automatic transmission. The truck has only 64,000 miles on it and runs like a top. I tow a 21.5 foot fifth wheel with it and have been having problems with the transmission dropping into neutral at low speeds (around 5 mph). Last year, I took it to the dealer for roughly $4,000 in preventative maintenance, which included a transmission service. Last month, I was visiting a campground in Southern Oregon and, after several hours of highway speeds, I pulled into the campground and slowed for a speedbump. When I stepped on the gas again, the transmission acted like it was in neutral. After letting off the gas and stepping on the gas again, everything was fine. At the next speedbump, the transmission did it again. I experienced absolutely no other transmission shifting problems during the remainder of the two week trip. When I brought it home, I took it to a good GM mechanic who serviced the transmission again and upgraded to a TransGo shift kit. He said that the transmission looked excellent and showed no signs of wear and no metal shavings were found in the filter or fluid.
A few weeks later, I drove the truck to Montana, again towing my fifth wheel trailer. Again, no problems shifting on the drive out. When I was preparing to return home, I stopped to dump the trailer tanks and experienced the same transmission in neutral experience. I put the truck in Neutral and then back into Drive and everything went back to normal. I drove all the way home with no further problems. The GM mechanic is now recommending rebuilding the transmission. While I don't mind rebuilding the transmission (and beefing it up, due to towing a heavy trailer), I don't want to have a new transmission and the same frustrating transmission symptoms. Is there anyone out there that has experienced this symptom? Could it be the computer or shift linkage? I love the truck and plan to keep it but I want to be able to count on it getting me to my destination and back. In addition, I hate having unfamiliar mechanics working on my truck when I am travelling.

 

Start by unplugging the harness at the pass through connector for the solenoids on the valve body. Inspect for transmission fluid in the connector. If it’s present, the internal wiring harness needs to be replaced because the connector seal is leaking. Cleaning it will provide a temporary fix.

 

@Gumby22 , are you saying that transmission fluid leaking past the solenoid pass through connector seal can cause the transmission to briefly go into neutral? Can you share the symptoms with me?

Thank you!

 

The symptoms are exactly as you describe - intermittently the transmission will act as if it’s in neutral, then it resumes normal operation. It can happen anytime - at startup or after driving. Codes may or may not be set.

There are also a couple of TSB’s recommending replacement of internal parts for similar concerns, but the fluid leaking through the connector seal is a known issue and the easiest to diagnose and repair. If there’s no fluid in the connector, it’s likely the transmission needs internal repair.

 

@gumby22 Thanks for the quick feedback. I will forward your diagnostics to my mechanic. As I said, I don't mind having a transmission rebuild but I just want to identify the problem first. Your information has been very helpful. Thank you.