Circuit/System Description

The 4WD LO indicator circuit consists of a light emitting diode (LED) feed circuit, a LED and a LED control circuit. The indicator dimming control circuit is the LED feed circuit and continuously supplies B+ to the 2WD HI, 4WD Auto, 4WD HI and 4WD LO LEDs. When the 4WD LO mode has been selected by the driver, the transfer case shift control module (TCCM) provides a ground through the 4WD LO indicator control circuit illuminating the LED.

The TCCM tests the 4WD LO indicator circuit for unexpected voltage by monitoring the B+ supplied by the BCM on the indicator dimming control circuit by grounding the 4WD LO indicator control circuit for 2 seconds during the Bulb Test at key ON.