I have a 2000 Chevy Blazer and after using the 4 wheel drive for the first time in a while now it switches by itself driving at any speed down the road without being touched and was it engages will not disengage back to too high
Your Blazer has a vacuum switch inside the transfer case that can fail which can cause the vacuum to leak pass the seals in the switch which will apply vacuum to the front axle actuator. When this happens, the front axle becomes locked to the front differential which is what essentially puts your car into 4x4. The part is relatively cheap to replace, however, the job itself can be quite complicated. I would recommend having an expert from YourMechanic come to your location to inspect the system in order to verify the problem and guide you with the repair.
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