4wd wont work on 1999 chevy tracker but front drive shaft is turning?
The locking hub control system is not engaging properly. On the 99 Tracker this is a compressed air system that consists of an air pump (compressor), electrical wiring to power and control the air pump, and air hoses that lead to an actuator inside the front differential housing. If there is a leak in the system the PCM will run the air pump for 10 seconds and then shut off, and your propeller shaft can turn all day long, but the front axles will remain free floating. Turn on your key, not your engine, and engage four wheel high. Go listen near the passenger front bumper for the air compressor. If you hear it, then the compressor control and the compressor itself are likely fine. If it shuts off after 10 secs or so, and your 4WD light isn’t on, the PCM timed out the compressor out and shut the compressor off to protect it. You will have to find the leak and fix it. If you are lucky, it’s the air line leading to the front differential; and not the air line inside the differential housing, or the air bladder in the locking actuator, which also resides inside the font diff. If the compressor shuts off and the 4WD light is on (this means the PCM did not shut the air compressor off due to timeout, so the pressure switch read 5-7 psi and the pump shut itself off), you likely don’t have a leak, and something mechanical has the actuator hung up inside the front differential. Lastly if you don't hear the compressor run at all, you either have a faulty compressor, or some sort of wiring problem in that circuit.....it could be as simple as a blown fuse. Good luck.
on Sep 28, 2013