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2006 chevy trailblazer_ls_ext
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5 Posts
Discussion Starter #1
I have been reading other posts about probs with the switch on the dash and/or the TCCM, but what led to repairing/replacing either of those isn't similar to the issue i have.

About 2 weeks ago, i turned my truck on and the light on the switch showed it was in 4hi, but the switch was pointing to 2hi. I can turn it to auto and it will switch, but when i turn the switch to 2hi, the light will blink numerous times and then the light for 4hi comes on again. The truck is def engaged in 4wheel drive.

Any suggestions??? Anything would be appreciated. Thanks!
 

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2006 chevy trailblazer_lt
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3 Posts
Could be tc shifter motor stuck in 4wd this would not allow you to shift back into 2wd.When you turn the selector switch you should here a distinct noise under the passenger floor of the vehicle.This is the tc shifter motor doing its job.
 

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2002 chevy trailblazer_ltz
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49 Posts
I had my switch do something similar to this. I disconnected the battery for a few minutes and it reset and has been woorking for the past year. Try the simple stuff first. Good luck!
 

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2002 chevy trailblazer_lt_ext
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295 Posts
Did you try pulling the fuse for 1 minute and putting back? Try rotating the knob a couple of dozen times, whith the engine off. The Roadie is the expert on this, but the switch is not expensive, I would change this befoe moveing on to the next step, encoder motor. When did you last do a fluid change on the t/c?
 

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2004 gmc
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26,181 Posts
No need to disconnect the battery to reset the system, and that has unintended (and risky!) side effects. Just pull fuse #8 in the front fuse block for 30 seconds.

Any time the system tries to go into a mode the switch isn't pointing to, the switch and its wiring are suspect. They do get dirty and go bad, and were redesigned around 2005-2006 for better reliability. So for a first experiment I'd just turn the switch CW and CCW with the ignition off 50-100 times to see if that cleans up the contacts.

Does the transition to 4LO work OK? Remember you have to have the shifter in neutral to do that.

Do you have any local buddies to swap switches with? Even if you have to get one from the dealer, they aren't that expensive after the redesign. GM #25965895. $28 list. $19 from parts4chevys.com
 

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2006 chevy trailblazer_ls_ext
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5 Posts
Discussion Starter #7
Thanks guys. So, i got a new switch from a dealer and it still did the same thing. I am thinking the actuator/control motor is bad as mentioned previously. Is there any way to check that directly, while its on the truck, or is changing it the only way to find out? where is that located at exactly? Will not switch into 4LO either. Any help would be greatly appreciated.
 

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2002 chevy trailblazer_ltz
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2,063 Posts
When you try to switch it into 4Lo, are you in neutral or park? If you are in gear, it will NOT go into 4Lo.

Matt
 

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2002 gmc envoy_slt
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349 Posts
From the service manual, for the NP8 transfer case:

"Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

The transfer case brake control is supplied voltage at all times, with the key ON, through the B+ circuit. The brake control is activated when the transfer case shift control module registers the following modes:
• AUTO FWD
• 4HI
• 4LO
This is accomplished when the transfer case shift control module provides ground to the brake control through the T-Case Lock circuit. If there is a fault in the brake control circuit, the transfer case shift control module goes into a shift block mode. The shift block mode causes the mode indicator to flash for 10 seconds when another mode is selected. After the 10 second period has ended, the indicator reverts back to the previous mode selection."


The T-Case Lock circuit includes:
• Battery power provided by an orange wire from Fuse 8 into pin F of the Transfer Case Encoder Motor
• Low-side brake control provided by a tan wire that extends from pin G at the encoder motor to pin B2 of the 16-way black connector at the TCCM. This circuit also passes through the chassis Harness to I/P harness inline connector (38-way black connector, pin B1), in the underhood compartment to the right of the underhood fuse block.

It's also possible that you have a faulty TCCM or Transfer Case Encoder Motor.

Good luck...
 

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2006 chevy trailblazer_ls_ext
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Discussion Starter #10
Thanks vball61. That is exactly what is going on. Any way to fix that? Replacing wires? Having TCCM reporgrammed?
 

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2002 gmc envoy_slt
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349 Posts
Is your "SERVICE 4WD" indicator lighting up on your dash? It should be, if you have the transfer case lock control circuit malfunction described above. If not, then I'd look at the TCCM first as the possible source of your problems.

If you're seeing the indicator, then the first thing I'd do is check out the wiring (provided you have a multimeter and know how to use it).
Check for:
  • Battery voltage at the orange wire into pin F of the Transfer Case Encoder Motor.
  • Continuity on the tan wire that extends from pin G at the encoder motor, to pin B2 of the 16-way black connector at the TCCM. Also make sure this circuit isn't shorted to ground.
If the wiring checks out, or you're not able to investigate the wiring, then I'd suggest either: a) temporarily swapping out your TCCM with a known good one (if you have access to one), to see if that fixes your problem, or b) take your truck to a dealer or knowledgeable repair shop for a more detailed diagnosis. There are a number of diagnostic trouble codes (DTCs) that can be set by the TCCM that can't necessarily be read out by a standard OBDII code reader.
 

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gmc trailblazer_ltz
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18 Posts
Hi
Have you been able to fix your 4x4 issue?? I'm having almost the same issues!! The other day out for a drive the service 4wd light came on and the 4hi indicator light was flashing on selector switch (knob was on 2hi) and it switched into 4wd hi mode while driving!!!! Pulled over and played with selector switch it went back into 2hi, turned off vehicle, restarted and service 4wd light went out. Have you been able to fix the issue on your trailblazer??
thanks
:worried:
 

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2006 chevy trailblazer_ls_ext
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Discussion Starter #13
I havent had a chance to diagnose the problem yet. I will be sure to let everyone know when i do.

The 4WD service light is not on. Im looking to swap the control module before taking it to the dealer.
 
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