• | 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. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Ambient Light Sensor Signal | B2645 03 | B2645 07 | B2645 07 | -- |
Ambient Light Sensor Low Reference | -- | B2645 07 | -- | -- |
Low Beam Headlamp Supply Voltage | 3 | 1 | 2 | -- |
Left Headlamp Low Beam Voltage Supply | 2, 3 | 2, 3 | 4 | -- |
Right Headlamp Low Beam Voltage Supply | 2, 3 | 2, 3 | 4 | -- |
DRL Relay Control | 2 | 1 | 1 | -- |
Left Headlamp Low Beam Ground | -- | 3 | -- | -- |
Right Headlamp Low Beam ground | -- | 3 | -- | -- |
|
The ambient light sensor is a light sensitive transistor that varies the voltage signal to the body control module (BCM) based on outside lighting conditions. When the ambient light sensor indicates daytime conditions with engine running, the body control module (BCM) grounds the DRL relay control circuit, energizing the DRL relay. With the DRL relay energized, voltage is applied through the relay switch contacts, the DRL 1 fuse, and the DRL 2 fuse to the left and right low beam headlamps. Any function or condition that turns the headlamps ON will cancel DRL operation.
Headlights/Daytime Running Lights (DRL) Schematics
Lighting Systems Connector End Views
Ignition ON, observe the scan tool Ambient Light Sensor parameter voltage while carefully supplying sufficient light to simulate daylight conditions to the ambient light sensor. The voltage reading should be approximately 2-3.5 volts.
⇒ | If the test lamp illuminates, test the low beam supply voltage 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 test lamp does not illuminate, test the B+ 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. |
⇒ | If the headlamps do not illuminate, test the supply voltage circuit for an open/high resistance. If the circuit tests normal, test or replace the DRL fuse or the rear fuse block. |
⇒ | If the resistance is not within the specified range, replace the relay. |
• | 30 and 85 |
• | 30 and 86 |
• | 30 and 87 |
• | 85 and 87 |
⇒ | If not the specified value, replace the relay. |
⇒ | If greater than the specified range, replace the relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for BCM replacement, setup, and programming |