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2003 gmc envoy_slt_xl
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Discussion Starter · #1 ·
Hi all. You guys have helped me in the past and I hope you can again.

I'm a mechanic for a quality used car lot and we have had a couple Trailblazers come and go. One that we sold is coming back for me to repair and the complaint is that the 4wd engages slowly and the owner says they have to rev the engine to get it to engage. This sounds weird to me but then again, these things sell faster than I have time to get to know them.

IIRC the TB in question is an '02 and has a 4.2L I-6. We installed a new TCCM and had it flashed at the dealer which brought the 4wd back from the dead.

So, apparently, it's working but not to the new owners satisfaction. Can someone give a brief summery of how the 4wd is engaged and how it's set-up?
 

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2004 gmc
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There are two motors that operate with the 4WD system. Revving the engine can have zero effect unless the voltage is low on the battery. The gauge should show that.

There is a front axle actuator that has a 2-3 second engagement time, and it only runs in a mode change from 2WD to A4WD and from A4WD to 2WD.

The transfer case has an encoder motor that makes a shorter and lower pitched noise on every mode transition.

You can listen for these with the ignition on, the engine off, and the tranny in neutral.

If the engagement time is too long to satisfy the TCCM, it will set the Service 4WD light on.

It could be that the customer is expecting the A4WD system to not require any time before engaging the transfer case clutches. This is not its design. It requires seeing slippage between the front and rear driveshafts, then engages the clutches. Often the front wheels start pulling with a lurch. This is the trailvoy standard operation, unless the TC clutches are really getting old and grabby, or the fluid needs changing.
 

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2003 gmc envoy_slt_xl
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34 Posts
Discussion Starter · #4 ·
I should have figured. Totally operator error and lack of understanding of 4 wheel drives. The guy was trying to shift to 4low while moving and in gear. Of course it would shift after switching to neutral in order to rev the engine.

The other complaint was wheels 'locking up' while in 4wd. DUH! It's a FOUR WHEEL DRIVE! Can't use it on dry pavement!
 

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2004 gmc
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Thanks for the report.

1) Assume you pointed the goofball to his Owner's Manual?

2) Also assume you pointed him to trailvoy as a resource. How harsh do you want us to treat this newb? ;) We've got a harshness scale of 1-10. :dielaugh:

 

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2003 gmc envoy_slt_xl
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Discussion Starter · #6 ·
I didn't get a chance to talk to the owner. One of the sales doofs told him but I doubt the information got relayed properly.
 

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2003 chevy trailblazer_lt
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just reading the first post y first thought was.. he is in gear and moving trying to into lo.. and i was rite lol...


bout the wheels locking up... please tell me where ur located so i can stay away from this guy..
 
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