Service 4wdrive I have a 2007 chev 2500HD new body style. The service 4wd warning comes on at start up. The 4x4 switch is illuminated however the indicator light is out. I checked the wires at the back of the switch with a test light and found juice going to two wires (cream coloured wire and a purple with white stripe). One has a very faint current(purple with white stripe) so I'm sure this is the problem. Any ideas what the problem might be?

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!st of all, I really hope you are NOT driving on dry pavement with your 4x4 engaged. 2nd if you're trying to engage the 4x4 and your getting the service 4x4 light, it's telling you that it will not engage the 4x4. Hook up a code reader to your ECU and find out what's up. More than likely if you have the push button 4x4, your servo motor to engage the 4x4 is not working. If you're mechanically inclined buy a service manual and dig in, if not take it to the GM dealer before it becomes totally FUBARED

To start with, a basic engine computer code reader will not connect to the body computer which is why they are not getting any codes.
The 4wd lights will not come on as long as the warning light is on, the system is disabled until it is fixed.
You may need someone with a professional scanner to connect to the body computer.

Well your mistake was letting them work on it they like to dink people around because they know whats wrong with there computer gadget my thoughts are the plug for the switch try to pull it out and then when you have this issue see if you can wiiggle some wires to see if theres a faultly connection... by the way mechanics prey for and on people like you with multiple codes going for the ones they can claim as the problem even tho they haave had this same issue before but they wont tell you that

Well it could be the selector switch, but I doubt it.
Generally, the service light means something is not working that the computer controls. Solenoids and valves are a couple of possibilities.
The transfer case is shifted by solenoids commanded by the body computer based on the switch position on the dash.
You should be able to have a shop scan the body computer for trouble codes and proceed from there.
A basic code reader may not access the body computer.

2005 z71 Silverado v-8 4X4 not working.
Case History 07 09 13
Problem started with service 4wDrive message. It would come and go. Got worse as time went on. Then it got to All switch lights would only come on 3 seconds when key turned on and again when started for 3 seconds. Then no 4X4 and no lights. Researched on internet and noted problem was often solver by replacing control switch due to bad solder joints. Ordered new switch. Changed out with no change. Replaced old switch.
Went to AutoZone and checked codes. Had 4 codes B2725, B0790 (both Cleared) and Codes C0327 & C0040 (Both would not clear)
Next I decided before taking to the shop to try cleaning the contacts although I thought I was probably wasting my time. Went to radio shack and bought electronic contact cleaner spray.($9.98). Pulled 30 amp fuse under hood and raised vehicle. Disconnected plug on transfer case and sprayed contacts on both plugs(male & female). Thoroughly dried with compressed air and plugged back in. Just knew this wasn't going to fix it. Also sprayed both plugs on both sides of transfer case(Rear) (2 speed sensors I think). Anyway to make a long story short started up truck and all was normal:o) Every thing work fine and all lights and all modes work correctly. Hope you have this easy of fix to cure your 4X4 problem. [email protected]

either the encoder is bad or the complete encoder motor assembly. this motor and encoder is mounted on the left side of the transfer case. easy to change.
this is the most common problem with the gm electronic transfer case.

have someone beep horn while you look for it.

new body style or old?
old body you will see a pin on top of lamp assembly slide pin out and light will come out.
new body remove two 10mm bolts and lamp will come out

i had the same problem with my 03 silverado.it's a internal problem in the 4WD actuator.my truck would go in 4WD sometimes and some other times the service 4WD light would come on and it would not got in..after a while it wouldn't go in at all so i replaced the actuator and it fixed the problem..