Test I: The Front Axle Does Not Engage/Disengage Correctly

Test I: The Front Axle Does Not Engage/Disengage Correctly

CAUTION: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multimeter probes.

I1:

I1-I4:

I4-I8:

I9-I11:

I11-I13:

I14-I15:

I15-I18:

I18-I20:

I20-I21:

I21-I22:

Normal Operation
When shifting between from 2H to 4H/4L, the 4x4 module supplies a timed ground path to the lock and lock/unlock solenoids to apply vacuum to the pulse vacuum hublocks (engaging the front hubs to the front axle). When shifting from 4H/4L to 2H, the 4x4 module supplies a timed ground path to the lock/unlock solenoid only (disengaging the front hubs from the front axle). Once the hubs are set to their intended state, they remain in that state until another timed vacuum "pulse" is delivered to the hublocks. Systematically check the necessary inputs and outputs at the 4x4 module, internal components of the transfer case, mode select switch (MSS), pulse vacuum hublocks (PVH) components and drive axles.

Possible Causes
^ Mode select switch (MSS)
^ Pulse vacuum hublocks (PVH)
^ PVH solenoid assembly
^ Transfer case
^ Vacuum leaks
^ Front axle assembly
^ 4wd control module (GEM)
^ Circuit 295 (GY/BK)
^ Circuit 605 (RD)
^ CJB fuses:
- 19 (10A)
- 27 (15A)
- 33 (15A)
- 45 (10A)