Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

4wd won;t engage

11K views 11 replies 5 participants last post by  TechNova 
#1 ·
04 Envoy. 90K miles.

when I turn the selector switch to 4wd the light flashes for 10 seconds and then goes back to a solid light for 2wd. I have tried it numerous times stopped and in motion.

I can hear the transfer case motor run, cannot hear the front motor.

I checked the fuse, including using a DVOM, the fuse was good.
I unhooked the front connector, the terminals are in perfect condition.

I checked the voltage and had 12 volts at the brown wire when I had someone turn the switch to 4wd. I had 12 volts for about 10 seconds.

This would indicate a bad front axle selector but a new one did not fix the problem.
I removed the selector, rotated each front tire individually and the front driveshaft did NOT turn. I used a screwdriver to push in on the "fork" in the housing. I could feel the fork move and when I pushed it in, rotating either front wheel caused the front driveshaft to turn.
Does anyone have any other ideas on what could be wrong?
 
See less See more
#4 ·
The brown wire should have 12V on it all the time with ignition on. Have you checked fuse #48 in the rear fuse box? If fuse is good, then you need to determine why the 12V disappears.

The Lt Blue wire is the control for the actuator, but if the 12V supply is not present, the actuator will not function.
 
#5 ·
The brown wire should have 12V on it all the time with ignition on. Have you checked fuse #48 in the rear fuse box? If fuse is good, then you need to determine why the 12V disappears. Maybe what you are measuring is a back feed from another source and the main 12V is not present at all.

The Lt Blue wire is the control for the actuator, but if the 12V supply is not present, the actuator will not function.
 
#9 ·
I believe the flashing is telling you that it can't engage the front axle disconnect. It's mechanical not electrical. That's what happened on mine. There are three rather light weight bearing inside it that when they fail they don't allow the shift collar to slide over the splines. There was a good discussion of it and how to diagnose front axle problems on GMTnation.com but I don't have the link. Sorry
 
#10 ·
It doesn't sound mechanical though if pushing the fork in manually engages the axle disconnect- and everything else seems tight? no play in cv/drive shafts/bearings?

maybe getting enough volts- but how about amps? just to try the simplest stuff first... I've had a couple of older cars where slow transmission shifting was one of the the first symptoms of a bad battery/connection
 
#12 ·
This one is causing my troubles. I checked the wires at the front axle actuator again, I have 12V at the brown wire with key on but cannot get 12V to the lt blue wire.
I have easy access to used parts so I tried another tccm that is located behind the light switch under the dash.
still same result, no 4wd.

This truck is really clean for our area but I still decided to clean the grounds on the left side of the engine. The terminal looked great even before I cleaned it.
The wires are good and the connectors do not have any bent terminals or corrosion. I still have no 4wd.


Any other suggestions? I am running out of ideas to check.
 
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