I have a problem only with 4-wheel Low?

2007 GMC ENVOY
190,500 MILES • 4.2L • 6 CYL • 4WD • AUTOMATIC
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STEVE620
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I do not use my 4-wheel drive except for snow that we just had. I think I have a problem only with 4-wheel Low going forward. When I engage it seems like it's slipping at first, I can see hear it then works like i think it should. backwards no problem and there is a big difference going backwards. I dropped it off at dealership and they told me it's working flawlessly I still have my doubts, what do you think before I take it elsewhere also before I took it in the dash light with the wrench and 4D service light was on and of course the light was out. And while driving it in the snow the selector knob light would not change until i would restart engine. Sorry if I'm all over the place here but as I remember I'm typing.
Thank you
Jan 24, 2024 at 7:27 AM
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STRAILER
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Hi Steve, with the wrench light on it should have trouble codes stored. let's go over this guide to retrieve the codes:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

To me it sounds like the transfer case encoder motor is getting weak and not commanding the shift fork inside. Here is how to change it out. Check out the images (below). Please let us know what happens.
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Jan 24, 2024 at 12:26 PM
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STEVE620
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I just used a code reader and I'm not getting any codes.
Jan 25, 2024 at 6:49 AM
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STRAILER
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Okay, I know a weak encoder motor can cause the transmission case not to shift correctly but I have also seen internal damage to the transfer case cause this problem as well. You might be able to remove the encoder motor and shift the transfer case by hand, or you can activate the motor once it is out of the case to see how it responds.
Jan 26, 2024 at 10:40 AM
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STEVE620
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Right now, the 4-wheel drive is working. When this first started to happen, I checked it with a code, and I just remembered the code I got was P0650.
Jan 26, 2024 at 1:56 PM
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STRAILER
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The P0650 code in a 2007 GMC Envoy is a diagnostic trouble code (DTC) related to the vehicle's Malfunction Indicator Lamp (MIL) control circuit.

So, I don't think this will cause an issue with the 4wd. Does the check engine light come on with the key?
Jan 27, 2024 at 10:41 AM
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STEVE620
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No lights are showing on dash and 4-wheel drive is working, everything looks normal. I will have to wait till another snow fall to see what happens.
Thank you
Jan 27, 2024 at 11:51 AM
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STRAILER
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Sounds good, please let me know. We should check all fuses with the key on, this guide can help:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here are the fuse locations. Check out the images (below). Please let us know what happens.

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Jan 28, 2024 at 10:37 AM