Lights On Indicator Malfunction

Lights On Indicator Malfunction

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview






Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies the voltage signal to the HVAC control module. The HVAC control module sends a signal to the body control module (BCM) via class 2 serial data commanding the BCM to apply ground to the headlamp low beam relay control circuit. This energizes the low beam relay, closing the switched side and applies battery voltage to the LEFT and RIGHT LOW BEAM fuses. Battery voltage is applied from the low beam fuses, through the low beam voltage supply circuits to the ballast in the headlamp assembly illuminating the headlamps. The BCM also sends a message via class 2 serial data to the instrument panel cluster (IPC) requesting the lights on indicator be illuminated. For more detailed information concerning headlamp operation refer to Exterior Lighting Systems Description and Operation.

Diagnostic Aids

This diagnostic procedure assumes that the headlamps operate as described in Exterior Lighting Systems Description and Operation.

Circuit/System Testing

Ignition ON, with a scan tool perform the display test for the instrument panel cluster (IPC) and observe the lights on indicator.

If the lights on indicator illuminates during the test, replace the BCM.
If the lights on indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Control Module References for BCM or IPC replacement, setup, and programming. Programming and Relearning