Lighting System Diagnosis

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
When the ignition is in the On position, the Body Control Module (BCM)supplies exterior lamp power to the high side of the park lamp relay coil. When the BCM receives an input from the headlamp switch to turn the park lamps ON, then the BCM grounds the park lamp relay coil, energizing the relay. When the park lamp relay is energized, battery power is supplied to the park lamps.

CONDITIONS FOR SETTING THE DTC
The BCM monitors the output to the park lamp relay every second at the park lamp control circuit. The criteria for the fault code to set is as follows:
^ Exterior lamp power is active.
^ A DTC B1970 is not set.
^ Headlamp switch is inactive.
^ The commanded state doesn't match the feedback for 3 seconds (open circuit, short to ground or B+).

ACTION TAKEN WHEN THE DTC SETS
^ The BCM continues to command the requested state until it is achieved or until it changes.
^ Stores a DTC B2476 in the BCM memory.

CONDITIONS FOR CLEARING THE DTC
^ The conditions for the fault are no longer present.
^ A history DTC will clear after 50 ignition cycles if the conditions for the fault is no longer present.
^ The use of a scan tool.

DIAGNOSTIC AIDS
Refer to Power Distribution Component Views in Wiring Systems for an end view and for terminal assignments of the relay box when the diagnostics direct you to take electrical measurements at the relay box.

Check for the following conditions if a history or intermittent DTC is indicated:
^ A intermittent open, or short to B+ in the park lamp relay control circuit or the headlamp switch redundant park lamp relay signal circuit.
^ A intermittent open in the exterior lamps power circuit.
^ A short to ground in the park lamp relay control circuit or the headlamp switch redundant park lamp relay signal circuit may cause the low beams to illuminate at all times with the ignition On and the headlamp switch in the Off position.
^ A damaged wiring harness. Inspect the wiring harness for damage. If the wiring harness appears to be in good condition, observe the display on the DMM while moving the connectors and wiring harnesses related to the circuits. A change in the DMM display during this test will indicate the location of the fault.
^ For additional information, refer to Inducing Intermittent Fault Conditions in Diagrams, Diagnostic Aids, Troubleshooting Tools.

TEST DESCRIPTION
The following numbers refer to the step numbers on the diagnostic table:
2. This step uses a scan tool to test the park lamp operation and to verify if the fault is present.
3. This step tests for voltage at the coil side feed of the park lamp relay.
4. This step verifies that the BCM is providing a ground signal to the park lamp relay.
5. This step tests if ground is being constantly applied to the park lamp relay.
14. After verifying that no circuit problems exist, the BCM is most likely at fault. The BCM needs to be programmed after installation.