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 |
|---|---|---|---|---|
Ambient Light Senor Signal | B2645 02 | B2645 05 | B2645 01 | -- |
Flash to Pass Switch Signal | 1 | 1 | 1 | -- |
DRL Relay Control | B2600 00 | B2600 00 | 2 | -- |
Headlamp High Beam Relay Control | B2580 06 | B2580 06 | B2580 01 | -- |
Headlamp Low Beam Relay Control | B2575 06 | B2575 06 | B2575 01 | -- |
LF Low Beam Headlamp Control | 1 | 1 | 1 | -- |
RF Low Beam Headlamp Control | 1 | 1 | 1 | -- |
Ambient Light Senor Low Reference | -- | 2 | 2 | -- |
LF Headlamp Ground | -- | 1 | -- | -- |
RF Headlamp Ground | -- | 1 | -- | -- |
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | -- |
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction | ||||
Circuit/System Description
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground and 5-volt reference signal to the ambient light sensor. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay control circuit. When the BCM applies ground to the relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL fuse to the left and right low beam headlamp control circuits illuminating the low beam headlamps. Any function or condition that turns on the headlamps will cancel DRL operation.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics
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, with a scan tool command the Headlamps On and OFF. The low beam headlamps should turn ON and OFF when changing between the commanded states.
- Ignition ON, park brake released, verify with a scan tool the Park Brake Switch parameter displays Inactive.
- Ignition ON, with a scan tool command the DRLs ON and OFF. The low beam headlamps should turn ON and OFF when changing between the commanded states.
| ⇒ | If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction. |
| ⇒ | If not the specified value, refer to Symptoms - Park Brake. |
| ⇒ | If the low beam headlamps do not turn ON and OFF when commanded, refer to Daytime Running Lamps Malfunction. |
| ⇒ | If the low beam headlamps turn ON and OFF when commanded, refer to Ambient Light Sensor Malfunction. |
Circuit/System Testing
Daytime Running Lamps Malfunction
- Ignition OFF, disconnect the DRL relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
- Connect a 15A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the low beam headlamps are activated.
- Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
- Command the DRL ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the DRL relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the DRL relay. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. |
| ⇒ | If the low beam headlamps do not activate, test the control circuit for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
Ambient Light Sensor Malfunction
- Ignition OFF, disconnect the harness connector at the ambient light sensor.
- Ignition OFF, scan tool OFF, doors CLOSED, test for less than 10 ohms between the appropriate low reference circuit terminal listed below and ground.
- If all circuits test normal, replace the ambient light sensor.
| • | Ambient light sensor low reference circuit terminal B - base |
| • | Ambient light sensor low reference circuit terminal C - uplevel |
| ⇒ | If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
