Test M: 4WD Does Not Engage at Speed Correctly

Test M: 4WD Does Not Engage At Speed Correctly

M1-M4:

Normal Operation
When the operator selects 4WD, the 4x4 module shifts the transfer case to 4H, which engages a dual-cone synchronizer clutch to synchronize the front and rear driveshafts, allowing a mechanical engagement of the transfer case. The 4x4 module also provides separate ground paths to the lock and lock/unlock solenoids. When the lock solenoid is engaged, a high level of vacuum is provided which rotates the hublocks to their "lock" position. When both the lock/unlock solenoids are engaged, a low level of vacuum is provided, which rotates the hublocks to their "unlocked" position. Systematically check the necessary inputs and outputs at the 4x4 module, internal components of the transfer case, PVH components and drive axles.

Possible Causes
^ Transfer case synchronizer
^ 4WD control module (GEM)
^ Front axle assembly
^ Circuit 779 (BN)
^ Circuit 92 (LB/YE)