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Q: 4hi intermittently won't engage.

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It is a electronic unit, with auto 4, 2, 4hi, 4 lo. Sometimes when I press the 4hi button the light comes on, it sounds like the actuator moves, but then the front wheels don't spin with the rear. 4lo works just fine, only the 4hi and auto 4 are the problem. It is an intermittent problem sometimes it is just fine.

My car has 180000 miles.
My car has an automatic transmission.

Hello there, many common faults will cause your 2006 Chevrolet Silverado to have intermittent four wheel drive engagement. The most common faults are the drive actuator, transfer case fluid level low, a wiring issue, or a selector switch that is failing. A qualified Technician such as one from YourMechanic will be able to diagnose your four wheel drive issues beginning with an inspection of the transfer case fluid level and then making any repairs required to resolve the issue.

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