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 |
|---|---|---|---|---|
Daytime Running Lamps Relay B+ -- North American | 1 | 1 | -- | -- |
Front Position Lamps Relay B+ -- European | 2 | 2 | -- | -- |
Ambient Light Sensor Signal | B2647 | B2648 | B2648 | -- |
Daytime Running Lamp Relay Control -- North American | 1 | 1 | 1 | -- |
Front Position Lamp Control -- European | 2 | 2 | 2 | -- |
Front Position Lamp Relay Control -- European | 2 | 2 | 2 | -- |
Front Position Lamp Ground -- European | -- | 2 | -- | -- |
Front Position Lamp Ground -- European | -- | 2 | -- | -- |
Headlamp Low Beam Ground -- North American | 1 | 1 | 1 | -- |
1. Daytime Running Lamps Malfunction 2. Front Positioning Lamp Malfunction | ||||
Circuit/System Description
North American
The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate. The DRL control circuit that supplies the low beam headlamp fuses with voltage contains a loop of wire that acts as resistance. This resistance is responsible for the low beam headlamps illuminating at a reduced intensity.
European
The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the front position lamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the front position lamp operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. The front position lamps will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, and the front position lamps will illuminate. The DRL control circuit that supplies the low beam headlamp fuses with voltage contains a loop of wire that acts as resistance. This resistance is responsible for the low beam headlamps illuminating at a reduced intensity.
Diagnostic Aids
Important: This diagnostic procedure assumes that the low beam headlamps are operating within specifications. If the low beam headlamps are inoperative, diagnose the low beam headlamp malfunction before proceeding with the following diagnostic. Refer to Headlamps Malfunction.
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 Testing
DRL Malfunction -- North American
- Ignition OFF, disconnect the DRL relay.
- Ignition ON, verify that a test lamp does not illuminate between the daytime running lamp 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 86 and ground.
- Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the DRL Status is On.
- Connect a test lamp between the B+ circuit terminal 85 and the relay control circuit terminal 86.
- Command the daytime running lamps 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 DRL 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 DRL headlamps are not on, test the control circuit terminal 87 for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit terminal 86 for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF, test the control circuit terminal 86 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
DRL Malfunction -- European
- Ignition OFF, disconnect the FRT POSITON LMP Relay.
- Ignition ON, verify that a test lamp does not illuminate between the front position lamp 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 86 and ground.
- Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the DRL Status is On.
- Connect a test lamp between the B+ circuit terminal 85 and the relay control circuit terminal 86.
- Command the DRL Status 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 FRT POSITON LMP 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 FRT POSITON LMP circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the FRT POSITON LMP relay. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. |
| ⇒ | If the front position lamps are not on, test the control circuit terminal 87 for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit terminal 86 for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF, test the control circuit terminal 86 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, programming, and setup
