• | 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 |
---|---|---|---|---|
HDM Relay B+ | 2 | 2 | -- | -- |
Ambient Light Sensor Signal | B2645 00 | B2645 00 | B2645 00 | -- |
HDM Relay Control | B2575 00 | B2575 00 | B2575 00 | -- |
Low Beam Headlamp Control | 2 | 2 | 2 | -- |
Ambient Light Sensor Low Reference | 1 | B2645 00 | 1 | -- |
HDM Relay Ground | -- | 2 | -- | -- |
Headlamp Ground | -- | 3 | -- | -- |
1. Daytime Running Lamp Malfunction 2. Headlamp Malfunction - Low Beam 3. Headlamp Switch Malfunction |
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) through the HDM using the reduced output or the headlamps at full intensity for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. The daytime running lamps (DRL) are the low beam headlights at a reduced intensity. With the headlight switch in the OFF 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 BCM signals the HDM for DRL operation in daylight conditions, the HDM illuminates the low beam headlights at a reduced intensity. The DRL will operate when the ignition switch is in the RUN 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.
Headlights/Daytime Running Lights (DRL) Schematics
Exterior Lighting Systems Description and Operation
Control Module References for scan tool information
⇒ | If the reading does not change between light and dark, refer to the Ambient Light Sensor Malfunction. |
⇒ | If the daytime running lamps do not turn ON and OFF, refer to the Daytime Running Lamps Malfunction. |
• | Ambient light sensor terminal B - manual heater controls |
• | Ambient light/sunload sensor terminal C - automatic heater controls |
⇒ | If the test lamp does not illuminate, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM. |
• | Ambient light sensor terminal A to B - manual heater controls |
• | Ambient light/sunload sensor terminal D to C - automatic heater controls |
⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
⇒ | 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 low beam headlamp control circuit terminal 4 for a short to ground. |
⇒ | If more than the specified value, test the ground circuit for an open/high resistance. |
⇒ | If the low beam headlamps do not illuminate, test the control circuit for a short to ground or an open/high resistance. |
⇒ | If only one low beam headlamp illuminates, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative low beam headlamp. |
⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for BCM replacement, programming, and setup |