Transfer Case Circuit Description

There are 2 main components for the 4WD system, Powertrain Control Module (PCM) and the front drive axle actuator pump, which is controlled by the PCM. Actuator pump compresses air to engage front axle. When transfer case is in 4WD (4H or 4L), the 4WD switch closes providing a ground signal to the PCM. The PCM actuates the pump which pressurizes actuator in front axle. Air pressure engages axle hub which connects front drive shaft to axle shafts, allowing transmission/transfer case to turn front wheels. PCM will not operate pump for more than 10 seconds at a time to protect pump. PCM will also provide a path to ground for 4WD indicator in instrument cluster. 4WD indicator light is provided battery voltage when ignition switch is in ON or START position through the IG fuse.

When transfer case is placed in 2WD mode, release valve in pump opens and releases air pressure in actuator. Without air pressure, the hub disengages. PCM also opens ground circuit to 4WD indicator light which causes indicator light to turn off.

On automatic transmission models, when transfer case is in 4L, the 4WD Low switch sends a ground signal to PCM, and PCM will not engage torque converter clutch.