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 |
|---|---|---|---|---|
Low Beam Headlamp Supply Voltage | 1 | 1 | 3 | -- |
High Beam Headlamp Supply Voltage | 2 | 2 | 4 | -- |
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | -- |
Headlamp High Beam Relay Control | 2 | 2 | B2580 00 | -- |
Headlamp Switch Headlamps Off Signal | B257A 00 | 6 | 6* | -- |
Headlamp Switch Headlamps On Signal | B257A 00 | 1 | 1* | -- |
Flash to Pass Switch Signal | 4 | 5 | 5* | -- |
Headlamp Dimmer Switch High Beam Signal | 4 | 2 | 2* | -- |
Low Beam Headlamp Ground | -- | 1 | 1 | -- |
High Beam Headlamp Ground | -- | 2 | 2 | -- |
Headlamp Switch Ground | -- | 1, 2 | 1, 2 | -- |
Turn Signal/Multifunction Switch Ground | -- | 2, 5 | 2, 5 | -- |
* Internal damage to the switch may occur if shorted to B+
| ||||
Circuit/System Description
Ground is provided to the headlamp switch through the switch ground circuit and G304. 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
Displays and Gages Connector End Views
Electrical Information Reference
Scan Tool Reference
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
