Test H: The Front Axles Do Not Engage/Disengage Correctly

Pinpoint Test H: The Front Axles Do Not Engage/Disengage Correctly

Normal Operation
When shifting between from two wheel drive high (2WD) to four wheel drive high (4X4 High)/four wheel drive low (4X4 Low), the 4X4 control module supplies a timed ground path to the lock and lock/unlock solenoids to apply vacuum to the pulse vacuum hublocks (PVH) (engaging the front hubs to the front axle). When shifting from 4X4 High/4X4 Low to 2WD, the 4X4 control 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 control module, internal components of the transfer case, mode select switch (MSS), PVH components and drive axles.

This pinpoint test is intended to diagnose the following:
^ MSS
^ PVH
^ PVH solenoid assembly
^ Transfer case
^ Vacuum system
^ Front axle assembly
^ 4X4 control module
^ Circuitry

H1-H2:

H2 (Continued)-H6:

H6 (Continued)-H10:

H10 (Continued)-H11:

H12-H14:

H14 (Continued)-H17:

H18-H20:

H20 (Continued)-H21:

H21 (Continued)-H22:

H22 (Continued)-H24:

H25-H26: