Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 6 of 6 Posts

·
Registered
2003 gmc envoy_sle
Joined
·
8 Posts
Discussion Starter · #1 ·
I have done alot of research on here and have been trying to figure out why my service 4wd light is on. I have changed both sets of wires for the speed sensors as per the tsb I found.These wires were badly corroded. Recently I found a short in the red wire going to the encoder motor.It was being pinched between the floor and the fuel lines.This caused the 25 amp fuse to blow under the hood.Now my service 4wd light is still coming on.It does not come on as a result of switching positions but rather just driving.It goes on and off and I cannot figure out why .I am thinking now it might be one of the speed sensors on the transfer case.I am trying everything not to bring it to the dealer for a $$ repair.
 

·
Banned
2004 gmc
Joined
·
26,436 Posts
Please fill out your profile so we know what we're dealing with here.

Does it properly go into and out of all modes with the expected noises from the encoder motor and the front axle actuator?

The dealer's scan tool can talk to the TCCM and get more information, including whether it's a sensor issue still or not. Or you can call around for an independent mechanic who has a high end scan tool to do the same. Have them troubleshoot it, then you do the repair.
 

·
Registered
2003 gmc envoy_sle
Joined
·
8 Posts
It did shift normally until today with all the expected sounds ie. Front actuator and encoder motor. But I noticed a whining coming from the encoder motor before and after it actually shifted.The encoder motor was changed a year ago with one I bought off ebay.

Roadie, Would you have a wiring diagram for the 4wd system? I want to make sure the red wire I replaced doesn't branch off anywhere. I Spliced from the plug at the encoder motor to the main harness beside the battery under the hood.
 

·
Banned
2004 gmc
Joined
·
26,436 Posts
The whining before and after the encoder motor movement is an encoder motor brake. Just to make sure it's locked into position in case of a single component failure in the TCCM. Otherwise a single failure could slam you into 4HI or 4LO without the logic interlock saving you. In 2002, I think, they didn't have this feature and must have had some incidents.

It's the essential difference between the 5-pin and the 7-pin encoder motors.

I'll scan the schematics tomorrow. Pressed for time tonight. Sorry.
 

·
Registered
2004 chevy trailblazer_ls
Joined
·
49 Posts
Service four wheel drive light!

My service light for my 4 wheel has been on for a while. I just replaced the TCCM and lights off but no action and truck now locked in 4lo. So do I need to replace the switch or get the TCCM program by the dealer first?
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top