4x4 wont engage No light illuminated on dial/switch - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > 4x4 Drivetrain

4x4 Drivetrain 4x4 Repairs & Problems

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  #1  
Old 02-09-2013, 02:51 PM
adamjalexander adamjalexander is offline
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Exclamation 4x4 wont engage No light illuminated on dial/switch

Hello!
I just bought a 2002 Trailblazer ltz 4x4 yesterday, 4x4 wont engage but knew this buying it, got a good deal. The whole transfercase was rebuilt 2 years ago/20k miles ago. The switch doesn't show if it is in 2hi a4 4hi or 4 lo, but it is in 2hi. I can turn the switch and nothing happens. No codes came up when read. What could the problem be?
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  #2  
Old 02-09-2013, 03:57 PM
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The 2002 model year had problems with the Transfer Case Control Module (TCCM) going to sleep or going stupid. Try pulling the #8 fuse in the underhood fuse panel for a minute and reinstall. If that doesn't revive it, you may want to look for replacement at a salvage yard, make sure you get one from a 2003+ vehicle.
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Old 02-09-2013, 04:47 PM
adamjalexander adamjalexander is offline
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thank you for your help, will try that. I have the truck in sweden, so will be hard to find a trailblazer/envoy at a junkyard. If i need new tccm I will get it online or when im back in Us.
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Old 02-10-2013, 05:42 AM
adamjalexander adamjalexander is offline
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Pulled the fuse , and it worked now the light is on, and it lets me put it in all modes but still only drives on 2. When I put it in lo I can hear it , but still only 2wd. What should I check next?
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Old 02-10-2013, 09:31 AM
keith20mm keith20mm is offline
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Quote:
Originally Posted by adamjalexander View Post
Pulled the fuse , and it worked now the light is on, and it lets me put it in all modes but still only drives on 2. When I put it in lo I can hear it , but still only 2wd. What should I check next?
With key on engine off, in neutral do you hear the transfer case servo motor change as you move the selector switch position? It makes a short whine as it shifts the transfer case. In fact, it is gear motor design, hence applies a good deal of torque even with its small size and low voltage. The transfer case control module runs the motor, in or out, to several positions.

There is also a position sensor in the servo motor unit.

You can read the position sensor , just a rotary potentiometer, using ohmmeter.
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Old 02-11-2013, 06:55 AM
adamjalexander adamjalexander is offline
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I did like you said, i could hear the tc putting it different modes, a4wd 4hi 4 lo one back to 2 hi. It all seems good but doesn't drive the front wheels still.
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Old 02-11-2013, 12:48 PM
adamjalexander adamjalexander is offline
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lifted the car and put it in 4 hi and driveshaft was spinning to front axel, so i guess it's either the acuator or the (pin) that locks in front axle? Correct me if i'm wrong
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Old 02-11-2013, 04:22 PM
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Without a load on the front wheels, the front driveshaft can still spin even if TC is not functioning properly. When you switch from 2WD to 4WD do you hear two distinct motor noises, one is a higher pitch than the other. These are the actuators at the TC and the Spline Disconnect at the passenger side front axle area.
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Old 02-12-2013, 09:12 AM
keith20mm keith20mm is offline
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Quote:
Originally Posted by adamjalexander View Post
lifted the car and put it in 4 hi and driveshaft was spinning to front axel, so i guess it's either the acuator or the (pin) that locks in front axle? Correct me if i'm wrong
The servo motor selects three 'hard' positions (4hi, 4lo, and 4off) and one 'soft' position (auto4). In auto4, a variable amount of torque is created by the servo motor varying force on a lever. For the moment, lets ignore the variable setting and focus on the manual positions (no 4, lo, hi)

To first verify that the motor actually did something, I removed the servo motor. This is just four hex head screws (12mm or so socket), then jiggle the motor unit until it pulled off the splined shaft. I then got all 4 wheels off the ground, and got an assistant to rotate wheels, front and rear, while I had a pair of vise grips clamped onto the splined stub (witha rag between jaws and grips). So I rotated stub CCW and checked front engagement, then back to neutral, then CW again to check other engagement.

This showed me that all 3 hard positions were doing something.

Return stub to beginning position before replacing servo.

If the transfer case is actually selecting the 3 hard settings for output to the front axle, then read this post next:

(How to change a 4wd actuator)
http://forums.trailvoy.com/showthread.php?t=80683
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Old 02-18-2013, 02:24 PM
adamjalexander adamjalexander is offline
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2002 Chevy TrailBlazer LTZ
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I have checked that tc works properly. And took out the front actuator and it works fine, so I pressed it in manually to make sure it was pushed in, had a helper who put it in drive and let the brake go, came a loud grinding noise from differential like it was trying to engage but couldn't.
Any suggestions what to do? Never worked on this kind of front axle before.
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