- 4WD LO Indicator Circuit Short to Ground or Open
Diagnostic Fault Information
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.
Conditions for Running the DTC
B0780 01
* Ignition ON
* System voltage 10-18 V
* Instrument panel lights not dimmed.
* Daylight running lights MUST be commanded ON.
* Circuit tested when the 4WD LO indicator is commanded ON.
B0780 06
* Ignition ON
* System voltage 10-18 V
* Instrument panel lights not dimmed.
* Daylight running lights MUST be commanded ON.
* Circuit tested when the 4WD LO indicator is commanded OFF.
Conditions for Setting the DTC
B0780 01
The TCCM detects 3.4 V or greater on the 4WD LO indicator control circuit when the 4WD LO indicator is commanded ON.
B0780 06
The TCCM detects 1.6 V or less for 1.5 seconds on the 4WD LO indicator control circuit when the 4WD LO indicator is commanded OFF.
Action Taken When the DTC Sets
Normal operation, the SERVICE 4WD indicator is not commanded ON. Driver is informed of fault via bulb inspection.
Conditions for Clearing the DTC
* The TCCM clears the DTC once the condition for setting the DTC is no longer present.
* A history DTC clears after 40 consecutive warm-up cycles without a fault present.
* History DTCs can be cleared using a scan tool.
Diagnostic Aids
* A TRUE B+ has enough current to light a test light.
* A DIAGNOSTIC B+ is a low current circuit that DOES NOT have enough current to light a test light.
* A short to ground on the 4WD LO indicator control circuit will cause the 4WD LO indicator to remain ON at all times.
* An open or high resistance will cause the 4WD LO indicator to be inoperative during the 2 second bulb inspection.
* An open in the indicator dimming control circuit will cause the 2WD HI, 4WD Auto, 4WD HI and 4WD LO mode indicators to be inoperative
during the 2 second bulb inspection.
* EL-49741 - harness is a good source for 9 V.
* EL-49742 - harness is a good source for B+ and ground.
* With key REMOVED - opening a door puts a true B+ on the indicator dimming control circuit, TCSCS X1 pin 4. Other possible voltages are
