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4x4 light

Have a 99 Dodge Durango. It is a good SUV. The only issue I have is that my part time 4 wheel drive light is always on. It has 165000 miles on it. Some times the transmission slips.

The vacuum switch is a known weak point. The switch is a little tower on the transfer case with four lines coming from it. The switch is activated by the transfer case when a lever inside the case presses a plunger at the base of the switch. Then, a spring in the switch extends the plunger when the lever is retracted. The problem is that the plunger is rounded to ease the lever’s action. This rounded part can be easily jammed inside the switch by the standard gunk in the transfer case. When this happens, the interlock and the 4WD light will not disengage. It is an easy fix by just un screwing the switch and cleaning it, but when it happens, you can feel the extra drag of the front driveshaft and associated parts.