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I have a 2005 Trailblazer EXT V8 with 80,000 miles on it. Without any prior 4WD issues, my service 4WD came on. When I tried to select anything other than 2WD the switch just blinks and I can hear it trying to engage then kicking back out. I took it to the dealer with the diagnosis of TCCM. Replaced that and had it programmed, still no 4WD. The dealer then said since there was previously no power to the TCCM it only gave that code. Now that the TCCM has power it is indicating the actuator needs to be replaced. After replacing the actuator myself still no change in the 4WD condition. I am sick of wasting my time at the dealer hooked up their computer and still no fix. Any suggestions?
 

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The dealer didn't give any guarantee that the TCCM diagnosis was correct? What idiots!

Anyway, if you do an advanced search here for posts mentioning "actuator" that are written by me "the roadie", you will read about how to diagnose the noises that two motors make. The encoder motor is different from the front axle actuator, and each one can fail in ways to light up the "service 4WD lamp.

Find those posts (many written in the last 6-8 weeks) and then listen to the various noises, and then let us know what you hear when you attempt to do various mode transitions.

You may need to pull a fuse (mentioned in those posts) to reset the TCCM between attempts, since a failed mode transition sometimes (almost always) will set the light on and then the TCCM gives up.
 
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