Question about GMC Envoy

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The service 4wd light came on in my 2002 envoy.

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There are two motors under the vehicle. The front axle actuator moves ONLY during 2HI->A4WD and A4WD->2HI transitions. The transfer case encoder motor makes a lower pitched noise in every mode transition: 2HI->A4WD, A4WD->4HI, and 4HI->4LO, and the three transitions upwards.

If EITHER of the motors fails to do what the TCCM commands it to do, the switch light will flash and the Service 4WD light on the dash will come on.

If you're a DIY mechanic, you might look into them further, or just take it to a mechanic who knows our systems. The average mechanic is not going to know the theory of operation of the trailblazer/envoy 4x4 system, which is pretty unique in the industry

Posted on Mar 11, 2011

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Posted on Jan 02, 2017

GARYca
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SOURCE: 2002 envoy 4wd problem. clicking sound comes and

Clicking sound- Possible electronic fan clutch failing. This is a typical problem with the 4.2L I6. When you hear the clicking, open the hood and listen if its coming from the fan clutch on front of the engine. this could also cause abnormal engine and transmission cooling. As for the "N" light and 4wd issue, have scanned at the dealer....Hopefully this helps

Posted on Jul 18, 2009

johnjohn2
  • 5763 Answers

SOURCE: My 2002 GMC envoy 4wd switch lights do not light

no, you may have a bad switch or 4wd module,i ve done afew that had bad switches, but i would check it before just replacing it,

Posted on Dec 13, 2009

  • 35 Answers

SOURCE: I Have a 2002 GMC Envoy that won't go into 4WD and

One of or all the of you switches are shot. You have one in the dash. One in the front end and one in the transfer case. More than likely it is one of or both the front end and transfer case in which if it is it is around $900 depending on the shop labor rate in your area

Posted on Jan 30, 2010

  • 177 Answers

SOURCE: i have 2002 envoy with service 4wd light on a code

Replace the transfer case module.this module will need to be programmed by a gm dealer.Co550 is a internal fault code.bulletin from gm for this.

Posted on Dec 02, 2010

  • 1 Answer

SOURCE: How to fix 4wd on 2002 envoy or problem shooting.

only way i can get it in to 4wheel is to put it in gear turn the 4 wheel switch to 4x4 hi or low and start the suv on and off until it kicks in to one of them ranges this is strange to me i put a new switch in the dash

Posted on Jan 05, 2011

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1 Answer

Why does the 4wd service light stay on


You need to check fluids or take to service at Chevy.

Feb 17, 2015 | 2002 GMC Envoy

1 Answer

Reset service indicator


When the 4WD Service light comes on it means that the Transfer Case Control Module (TCCM) has not received the proper feedback from the two actuators that control the 4WD engagement. The system needs to be diagnosed by a technician.

Apr 06, 2014 | 2003 GMC Envoy Xl

1 Answer

When I switch my 2002 envoy into 4wd it does not engage and 4wd service light comes on? How can I fix this problem as it worked fine before


This problem could be the Transfer Case actuator/motor or the spline disconnect assembly at the front differential, or a bad Transfer Case Control Module. The other important maintenance action that needs to happen every 50K miles is the transfer case fluid needs to be changed.
Repair of these item is probably not for a unintiated DIY'r.

Jan 21, 2013 | 2002 GMC Envoy

1 Answer

2002 envoy code co550


you need to replace the tccm and get it programmed.


2-04-21-006E: Inoperative 4WD/AWD Lamps, Inoperative 4WD/AWD System, DTC C0550 Set No Communication with TCCM (Reprogram Transfer Case Control Module) - (Jul 20, 2006)
999999995.gif Subject: Inoperative 4WD/AWD Lamps, Inoperative 4WD/AWD System, DTC C0550 Set, No Communication with TCCM (Reprogram Transfer Case Control Module) Models: 2004 Buick Rainier 2002-2004 Chevrolet TrailBlazer, TrailBlazer EXT 2003-2004 Chevrolet Avalanche, Silverado, Suburban, Tahoe 2002-2004 GMC Envoy, Envoy XL 2003-2004 GMC Sierra, Yukon, Yukon XL 2004 GMC Envoy XUV 2002-2004 Oldsmobile Bravada with Electronic Shift or Active Transfer Case (RPOs NP1, NP4 or NP8)

This bulletin is being revised to add Subject information and change the labor operation. This bulletin cancels and supersedes Bulletin Number 03-04-21-006. Please discard Corporate Bulletin Numbers 02-04-21-006D and 03-04-21-006 (Section 04 -- Driveline/Axle).
ConditionSome customers may comment that the 4WD/AWD indicator lights on the selector switch do not work, or the 4WD/AWD system may be inoperative and/or the service 4WD light is illuminated. The condition is typically intermittent and always occurs at key-up. Upon investigation, the technician may find DTC C0550 set.
CauseThe Transfer Case Control Module (TCCM) has not received the wake-up call during key-up and has remained in the "sleep mode".
When the TCCM is in the "sleep mode", it will not communicate with the class II bus or the Tech 2®.
Correction
  1. Try to communicate with the TCCM. If no communication, go to step 2. If communication is possible, go to step 5.
  2. Remove the underhood (ATCM or TREC) TCCM fuse.
  3. Wait 30 seconds.
  4. Reinstall the fuse. The module should "wake up" and communicate with the Tech 2®.
  5. Check for codes in the TCCM. If a C0550 is found current or in history with or without other codes, replace the module and go to step 6.
  6. Reprogram the TCCM with the latest TIS software using normal SPS procedures.
  7. Verify operation and that no codes are present.
Important: For the 2002 model year, the TCCM must be replaced and reprogrammed.
Warranty Information

Jul 29, 2011 | 2002 GMC Envoy

1 Answer

I have 2002 envoy with service 4wd light on a code co550 ecu/ccu malfunction .where do i go


Replace the transfer case module.this module will need to be programmed by a gm dealer.Co550 is a internal fault code.bulletin from gm for this.

Dec 02, 2010 | 2002 GMC Envoy

1 Answer

My 2002 GMC envoy 4wd switch lights do not light up at all, not even on start. The fuses are all fine. Is there some other power source?


no, you may have a bad switch or 4wd module,i ve done afew that had bad switches, but i would check it before just replacing it,

Dec 13, 2009 | 2002 GMC Envoy

1 Answer

My 2002 Envoy will not shift into 4 wheel drive or anything other than 2WD. The lights are not lighting up on the switch and the fuses have been checked and good. Any ideas?


check the transfer case selector motor, they go bad and thats what happens, no 4wd and no other lights on switch because its not doing any changing of the tranfer case, to test remove motor ground it and with connector connected, try to switch to 4wd see if motor moves, you can use a test light to make sure its getting power, hope this helps.

Dec 13, 2009 | 2002 GMC Envoy

1 Answer

2002 envoy 4wd problem. clicking sound comes and


Clicking sound- Possible electronic fan clutch failing. This is a typical problem with the 4.2L I6. When you hear the clicking, open the hood and listen if its coming from the fan clutch on front of the engine. this could also cause abnormal engine and transmission cooling. As for the "N" light and 4wd issue, have scanned at the dealer....Hopefully this helps

Jul 18, 2009 | 2002 GMC Envoy

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