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Discussion Starter #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?
 

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2004 gmc envoy_slt
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2,376 Posts
If you are saying that when a new front actuator was installed, the disconnect still did not engage. In that case there is either a wiring issue ot the TCCM is bad.
 

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Discussion Starter #3
I am getting 12V for about 10 seconds wen the switch is turned to 4wd.
wouldn't this indicate all is good with the wiring and the module.?
 

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2004 gmc envoy_slt
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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.
 

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2004 gmc envoy_slt
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2,376 Posts
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.
 

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Discussion Starter #6
I checked the fuse, it is good.

I need to recheck the wiring diagram, I had the lt brown as the switched 12V.
AllData doesn't let me expand the diagram very much. I will see if I have it in Mitchell or CCC where I can zoom more.
 

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2003 chevy trailblazer_lt_ext
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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
 

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2007 chevy
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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
 

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2003 gmc envoy_slt_xl
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I have a 2003 Envoy XL Slt 5.3 128000. I had the same issue. I replace the encoder motor. I purchase the part from ebay and installed it myself. Two bolts and your done. I was good to go and no more cycling on the selector.
Hope that helps you.
 

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Discussion Starter #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.
 
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