Engaged, then just kicked out. Has worked only couple times since
If the light comes on and you can hear the t-case engage, chances are the front diff is not locking in. The diff is locked in using a cable attached to a vacuum servo. This servo may be located under the battery tray and is operated by a vacuum supply that comes from the engine and goes to the t-case. When 4x4 is selected, a switch on the t-case allows vacuum to travel up to the servo and retract the cable allowing the front diff to lock in. You may have a vacuum issue to the servo or the servo itself may be defective. I have seen these leak/tear on a regular basis on older models
SOURCE: 1988 chevy 4x4 actuator
The switch for the 4wd light is on top of the transfer case. It is probably sticking
SOURCE: 1999 Chevy Silverado 4x4, transfercase will not kick out of 4x4
sounds like the punch solinoid in the front diff
SOURCE: 01 Chevy Silverado 4 X 4 not working. 4WD light
Having the same exact problem but with my 1999 escalade. Thought it was the actuator bought a new one installed it transfer case would engage but front end wouldnt lock. Took it out of housing left it plugged in got a friend to go through all the 4wd for me and the plunger never moved out the actuator. Checked my wiring harness which is a four prong ann it had one hot prong like it is suppose to. Traced wires even replaced dash switch same problem. Taking it to local dealership tom to have it checked for codes. I was told it could be the transfercase actuator even though its workin that actuator is what sends power to the front to engage the actuator to lock the differential.
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