Is a way to check the transfer-case four wheel drive actuator with encoder unit

DIANA ROGERS

MEMBER
2002 CHEVROLET TRAILBLAZER
4.2L
VR6
4WD
264,000 MILES

No lights on the dashboard selector switch, ( have all ready replaced), and the vehicle will not go into four wheel drive. Have all ready done research and believe that it is the actuator/encoder based on what I have found out. Research said to replace with ACDelco parts as aftermarket units may not fix problem where original part does. However, I would like to test the one I have before I replace it as it is $200.00 plus, and $30.00 core charge. Is there a way to test these to see if they work before I shell out $230.00 plus for the part? Thank you.

Thursday, January 4th, 2018 AT 5:51 AM

1 Reply

STEVE W.

MECHANIC
14,487 POSTS

If you have no lights on the four wheel drive switch the issue is probably not the encoder motor. It is more likely a faulty transfer case control module. That is because the lights get power from the TCCM.
One thing to try would be to go into the under hood fuse block and pull the ATC fuse, Keep it out for about ten minutes, then plug it back in and see if the TCCM wakes up.
If not take it to a shop that has a good scan tool and see if there are any stored codes in the TCCM, The TCCM in that truck was a problem item from day one, there are a couple of software updates for them as well.

As for testing the encoder itself, it is actually nothing more than a motor and switches to tell it when to stop. If you want to test if it is faulty just use a multi-meter to probe the red and black wires that feed power to the motor from the TCCM. When you push the switches the voltage should go on/off and the motor should move.
To do testing beyond that requires a Tech @ or similar scan tool that can control and monitor the outputs from the TCCM and the encoder.

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