Circuit Description

WARNING: This page is about a different car, the 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The indicator lamps circuit consist of 5 individual lamps contained inside the mode/range switch assembly. The following lamps are contained inside the respective range button:

AUTO 4WD
2HI
4HI
4LO

Each time the ignition is cycled, all 5 mode indicators light simultaneously, as an indicator check to ensure proper operation of the indicators. When the ignition is ON, the transfer case shift control module illuminates the indicator lamp that corresponds to the current ATC gear position, by providing a ground through a current limiting driver.

The transfer case shift control module flashes each indicator lamp after a shift has been requested and continues to flash until the transfer case shift control module completes the shift.

A solid state circuit, located inside the switch, supplies ignition voltage to the lamps. The solid state circuit also receives voltage when the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch, the circuit reduces the voltage that is supplied to the indicator lamps, dimming the lamps when the headlamps are ON.