Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Headlamp Dimmer Switch High Beam Signal | 3 | 3 | -- | -- |
Headlamp Switch Headlamps ON Signal | B257A 00, 1 | B257A 00, 1 | B257A 00, 1 | -- |
Headlamp Switch Headlamps OFF Signal | B257A 00, 1 | B257A 00, 1 | B257A 00, 1 | -- |
Flash to Pass Switch Signal | 4 | 4 | -- | -- |
Headlamp High Beam Relay Control | B2580 00, 3 | B2580 00, 3 | B2580 00, 3 | -- |
Headlamp Low Beam Relay Control | B2575 00, 2 | B2575 00, 2 | B2575 00, 2 | -- |
LF High Beam Headlamp Control | 3 | 3 | 3 | -- |
LF Low Beam Headlamp Control | 2 | 2 | 2 | -- |
RF High Beam Headlamp Control | 3 | 3 | 3 | -- |
RF Low Beam Headlamp Control | 2 | 2 | 2 | -- |
LF Headlamp Ground | -- | 2, 3 | 2, 3 | -- |
RF Headlamp Ground | -- | 2, 3 | 2, 3 | -- |
Turn Signal/Multifunction Switch Ground | -- | 3, 4 | -- | -- |
1. Headlamp Switch Malfunction 2. Headlamps Malfunction -- Low Beam 3. Headlamps Malfunction -- High Beam 4. Headlamps Flash to Pass Malfunction | ||||
Circuit/System Description
Ground is provided to the headlamp switch through the switch ground circuit and G202. With the headlamp switch in the ON position, the headlamps ON signal circuit from the body control module (BCM) is pulled low indicating the headlamps ON request. In response to this signal, the BCM will energize either the high or low beam relay illuminating the headlamps. At the same time when the high beam headlamps are ON, the BCM sends a message via GMLAN serial data to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. Anytime the headlamps are ON and the ignition is OFF or the driver door is opened, the BCM will also request the IPC to turn on the LIGHTS ON INDICATOR located in the driver information center (DIC).
Diagnostic Aids
This diagnostic procedure assumes that the headlamps operate as described in Exterior Lighting Systems Description and Operation.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, turn the headlamp switch to the headlamps ON position and observe the headlamps and the IPC headlamps On indicator. The headlamps and the headlamps On indicator should illuminate.
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 does not illuminate during the test or remains illuminated at all times, replace the IPC. |
| ⇒ | If the lights on indicator illuminates during the test, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for BCM or IPC replacement, setup, and programming
