Fluid Pressure Switch

I have a 2002 GMC Crewcab One Ton 4x4 with a Duramax in it. I pull a 28 ft Aluminum horse trailer that has a 14' custom living quarter in the front. Usually the weigh runs around 10K loaded. Last April, I had to replace the Tranmission Fluid Switch after an incident where I started the truck, pushed the Tow/haul button and the truck would only pull off in 3rd gear. Onstar read the code as 0700 as did the dealership. They replaced the swith and less than 8K miles later the same thing happened! The truck appeared to only have 3rd gear with no reverse. So while my friends and I were trying to figure out how to pull the truck and trailer backwards with the tractor, I cut the truck off. It was decided that I should try to pull forward a little to more to straighten up the rig. The problem had vanished and all gears were working normally. Go figure. I drove it home, called the dealership and took it in the next day. They pulled the dsame code 0700 and said the switch needed replacing AGAIN but would not be covered under any warranty since the truck had been over 12K miles since the switch had been replaced. I needed the truck the next week and could not take the chance it would not be ready. Well, that was over 2K miles ago and no more problems have occured. The tranny shifts great. So my questions are:
1) what caused thatswitch to default to 3rd gear?
2) why would it reset after turning the truck off and then not be a problem?
3) could it be that the tranny fluid was too cold?
4) could it be that I pushed the Tow?Haul button too soon after start up?
5) should I push the Tow/ haul after I have pulled off and not before?
6)since both times it was setting under the shed, was not quite level, and had not been driven in several weeks, could the tranny fluid be settling or gelling?
7) should I request another fluid change even though it just had it done at 15K miles ago?
8) Do you think it could be a fluid problem and not a fluid switch problem?

thanks in advance


Fluid Pressure Switch


Although I am not familar with the GMC Duremax, it sounds like you have an age old problem of loacl dealers not knowing what they are doing. As most local dealers are parts changers to say the least. Dealers should have done a little trouble shooting before just changing a part.

Look up your area customer service representative for GMC and lodge a complaint with them and ask the same questions. General Motors normally does a good job of protecting their own image.