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Discussion Starter #1 (Edited by Moderator)
Hi, my name is Dom and I'm new to this site. I have a 2002 GMC Envoy. I have the switch inside the vehicle to change between 2HI, AWD, 4HI, and 4LO. Sometimes when I start the vehicle the light in the transfer case consistantly blinks. When the transfer case is functioning properly, it will only blink when it is in transition from one to another. I can put the vehicle into 4LO and I can hear the hub caps lock into place, although i cannot tell if the vehicle is actually being activated into 4HI or AWD. The link below is a YouTube video I took of the transfer case flashing.

Any suggestions of fixes would be great and appreciated. Thank you very much.

 

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2004 gmc
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Welcome! This system is my specialty. I'm also going to move the thread to the 4X4 drivetrain section for more focus.

The TCCM (control module) is running diags all the time, and I bet what's gone slow is the front axle actuator. That's a higher pitched whine that lasts for 2-3 seconds and only runs when you go from 2WD->A4WD and vice versa. The transfer case encoder motor is a lower pitched noise that makes a sound at every mode transition.

If the feedback sensor circuit on either motor has a problem, the mode switch lamps will flash exactly like that.

To reset the TCCM, pull fuse #8 under the hood for ten seconds, then put it in, then put the ignition switch in RUN. Don't even need to start the car. Then go to A4WD mode and see if you hear a high pitched whine plus the lower pitched motor noise. If the whine takes too long (usually a problem with congealed grease in the actuator in the winter in cold locations) then the TCCM will fail the diagnostic and flash the mode lights.

In general, pulling fuse 8 will force the TCCM to run the diagnostics again instead of retaining the memory of the last failure, in which case it usually gives up and quits trying. You might need to pull and clean the connectors at the actuator and the transfer case encoder motor. Are you a DIY kind of person with tools and a meter?
 

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Discussion Starter #3
I am not a diy but I work at a car delear and I work around a bunch of techs and I'm going to print off what you posted and show one and have them do it. If it is just the fuse I can do it. Anything else I will have my tech do it. I'll Try it out tomorrow and let you know how it goes. Thank you very much.
 

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2004 chevy trailblazer_ls
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Welcome! This system is my specialty. I'm also going to move the thread to the 4X4 drivetrain section for more focus.

The TCCM (control module) is running diags all the time, and I bet what's gone slow is the front axle actuator. That's a higher pitched whine that lasts for 2-3 seconds and only runs when you go from 2WD->A4WD and vice versa. The transfer case encoder motor is a lower pitched noise that makes a sound at every mode transition.

If the feedback sensor circuit on either motor has a problem, the mode switch lamps will flash exactly like that.

To reset the TCCM, pull fuse #8 under the hood for ten seconds, then put it in, then put the ignition switch in RUN. Don't even need to start the car. Then go to A4WD mode and see if you hear a high pitched whine plus the lower pitched motor noise. If the whine takes too long (usually a problem with congealed grease in the actuator in the winter in cold locations) then the TCCM will fail the diagnostic and flash the mode lights.

In general, pulling fuse 8 will force the TCCM to run the diagnostics again instead of retaining the memory of the last failure, in which case it usually gives up and quits trying. You might need to pull and clean the connectors at the actuator and the transfer case encoder motor. Are you a DIY kind of person with tools and a meter?
You know the roadie is a smart guy when he tells the mechanics what to fix and how. :hail: :)
 
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