Circuit Description (Non-Active 4WD System)

The 4WD low circuit consists of a transfer case selector switch, Transfer Case PCM (TCCM) and wiring. When 4WD low is selected, TCCM receives a momentary signal from selector switch. If all conditions for 4WD low are met, TCCM allows electric motor in transfer case to perform shift. When 4WD low is engaged, voltage to PCM (PCM/VCM) changes from ignition voltage to zero volts. The 4WD low switch signal corrects transmission output speed signal to PCM/VCM. This signal compensates for transfer case gear reduction. The PCM/VCM uses transmission output speed signal to adjust shift points, line pressure and TCC scheduling. DTC P1875 is set if PCM/VCM detects a continuous open or short to ground in 4WD circuit.