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 |
|---|---|---|---|---|
Flash to Pass Switch Signal | 1 | 5 | 5 | -- |
Headlamp High Beam Relay Control Circuit | B2580 06 | B2580 06 | B2580 01 | -- |
Headlamp Dimmer Switch High Beam Signal | 1 | 2 | 2 | -- |
Headlamp Switch Headlamps On Signal | 1 | 4 | 4 | -- |
Headlamp Switch Headlamps Off Signal | 4 | 1 | 1 | -- |
Headlamp Switch Signal | 1 | 4 | 4 | -- |
Low Beam Relay Control | 1 | 3 | 3 | -- |
LF High Beam Headlamp Voltage Supply | 2 | 2 | 1 | -- |
LF Low Beam Headlamp Voltage Supply | 3 | 3 | 1 | -- |
RF High Beam Headlamp Voltage Supply | 2 | 2 | 1 | -- |
RF Low Beam Headlamp Voltage Supply | 3 | 3 | 1 | -- |
LF Headlamp Ground | -- | 4 | 4 | -- |
RF Headlamp Ground | -- | 4 | 4 | -- |
Turn Signal/Multifunction Switch Ground | -- | 4 | 4 | -- |
1. Headlamps Always On - Low or High Beams 2. Headlamps Inoperative - High Beams 3. Headlamps Inoperative - Low Beams 4. Headlamps Inoperative - Low and High Beams 5. Headlamps Inoperative - Flash to Pass | ||||
Circuit/System Description
With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G200. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to both relay switch circuits. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. The high beam headlamps are grounded at G104. The headlights may be switched to high beam with the movement of the headlamp dimmer switch lever. With the headlamp dimmer switch in the high beam position the BCM sends a message via GMLAN to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
High Beam Indicator Inoperative
Ignition ON, install a scan tool and command the high beam indicator ON.
| ⇒ | If the high beam indicator illuminates, replace the BCM. |
| ⇒ | If the high beam indicator does not illuminate, replace the IPC. |
High Beam Indicator Always On
- Ignition OFF.
- Replace the IPC.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for BCM and IPC replacement, setup, and programming
