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Q: 4WD is not engaging on my1997 Chevy Blazer

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I recently discovered that my 4wd has stopped functioning. I have replaced both the actuator under the battery tray and the actuator valve on the transfer case and is still non-functional. I can hear the transfer case switching to 4hi and 4lo but it does not lock the front differential. What is weird though is if I want to go over a curb, I can put in in 4lo and I can feel the front wheels pull the truck over the curb. But if the rear wheels spin, it immediately disengages. I tried to get out of a muddy field and I put it in 4hi then 4lo but only the rear wheels were spinning. I don't know what else to check. I really need the 4wd since I live in a snowy region. Any help is appreciated.

My car has 98000 miles.
My car has an automatic transmission.

Hi there. The problem with the transfer case can be caused by the encoder motor/transfer case motor loosing power, the transfer case engagement switch failing or loosing power, the vacuum actuator under battery tray loosing vacuum, the vacuum actuator valve leaking vacuum on the transfer case, or a broken cable from actuator to front differential.

Since you replaced the actuator under the battery and the actuator valve on the transfer case, then the problem lies within the motor on the transfer case, the transfer case engagement switch in the cab, or the cable that runs from the actuator to the front differential. Check the switch in the cab to make sure that it has power and is keeping power while in 4x4 mode. If there is power and the switch is okay, then check the motor on the transfer case to see if it is coming on.

Check for power on the harness to the motor and ground to the harness. If the harness is good and there is power and ground but the motor is not working, then replace the motor. If the motor is working, then you need to replace the cable to the front axles so it can engage and lock the front axle. If the cable is working fine, then you may need to have your transfer case rebuilt or replaced (if all options are exhausted). If you need further assistance diagnosing your transfer case, then seek out a professional, such as one from YourMechanic, to help you with your vehicle.

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