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Parts Expert
Parts Expert, Auto Parts Compnay Owner
Category: Car
Satisfied Customers: 6
Experience:  Over 20 years of Delership OEM auto parts experience. I Now Own My Own Auto Parts Company.
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2003 GMC: new one..My truck..engaging..gears

Resolved Question:

I have a 2003 GMC Sierra regular 2500 4wd pick-up truck. This is something wrong with the 4wd switch (which I have just replaced with a new one today) or something else is wrong with it! My truck is having serious problems identifying and engaging into the proper gears! F.Y.I. I had just replaced with a new Jasper transfer case and a new Jasper transmission both within the last year! My mechanic and I can't figure out what is wrong. His diagnostics box can't/won't tell him what's wrong. Please help!
Submitted: 7 years ago.
Category: Car
Expert:  Parts Expert replied 7 years ago.

Did you replace it with a Genuine GM transfer case switch, and is it the one one the dash? If you did Please give me the GM part number and i will verify it is correct, there are 2 different ones for your model.
Customer: replied 7 years ago.
Yes the switch is on the dash, to the left of the steering wheel. What is happening is when I start my truck the switch does not show the truck as being in 4wd. Yesterday and today (even after I replaced the switch with a new part from GM) the truck went from 2wd to 4wd while I was driving! It was incredibly high pitched and then clunk it dropped hard. Here is the part number I got from GM this morning 15136039. This is the only truck I have for work and I need it fixed. Its on the side of the road until my mechanic can tow it later today. Is this a module or maybe something as simple (or not so simple) as an electrical prob?
Expert:  Parts Expert replied 7 years ago.
Ok that switch is the correct one for your truck, and Since you got it form the GM dealer You can narrow it down that it is not the problem. The transfer case modules are also notorius for going out on these trucks, and will generally give no codes when they go out. This is most likely your problem. Teh most common symptom of the module going out are flashing erratic lights on the transfer case switch , or no lights at all. The high pitch you heard was teh case going into neutral, and the clunk is when it engaged suddenly. The newer control modules are much more reliable thatn the old ones and have all new software, so be sure to get a new one from a dealer, and not a used one of your will have the same problem.
Customer: replied 7 years ago.
I was thinking it was probably the modules. About how much do you think that would cost me to get control modules and would it be something I could do myself or should I have my mechanic do it?
Expert:  Parts Expert replied 7 years ago.
They usually run between 250 and 400.00, and they do have a core charge, so you will want to bring the old one with you or it will be $150.00 extra until you return the old one. If you want to try your luck you could try a used one for less, however you could run into the same problem. YOu can ge teh part number fom the dealer and then go to and get it a lot cheaper, jsut be careful theere shipping rates are a little high some times.
Customer: replied 7 years ago.
Is it fairly easy to install on my own or is it something my mechanic should do. Just tryin to save some $$$
Expert:  Parts Expert replied 7 years ago.
.On some models is is located in the kick panel or udner the dash of the truck and on others right above the transfer case . You can install it yourself, but ONLY if it does not require prgramming. the programming depends on the VIN number and not the module, so you will want to give your Loal Chevy dealer your VIN number oto see if it does or not. If it does you should get them either to install and program or just program it for you. Your local shop you are using may be able to program also if they have the right equpment.
Customer: replied 7 years ago.
Just talked to GM dealer near us. They are charging $630 for the powertrain control module! He did look up our vin and said that module would need programming. Thank you so much for your help. Wish us luck!
Expert:  Parts Expert replied 7 years ago.
Wow thats a lot, But he is looking up th ePCM, tell him you need the Transfer case module, They are 2 different things, the PCM just controls engine and transmission. the transfer case has its own module.
Customer: replied 7 years ago.
Ok we looked up the transfer case module like you said and price is $324. It also needs to be programmed. So we're stuck taking it to the dealer. Thanks again so much for your help!!
Expert:  Parts Expert replied 7 years ago.
Your welcome please click accept so I can get paid. Thanks
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