• | 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 |
---|---|---|---|---|
DRL Relay B+ | 2 | 2 | -- | -- |
Ambient Light Sensor Signal | B2645 03 | B2645 07 | B2645 07 | -- |
Daytime Running Lamps Control | 2 | 2 | B2600 00 | -- |
Headlamp - Left Front Low Beam Control | 1 | 1 | 1 | -- |
Headlamp - Right Front Low Beam Control | 1 | 1 | 1 | -- |
Ambient Light Sensor Ground | -- | B2645 07 | -- | -- |
Headlamp - Left Front Ground | -- | 1 | -- | -- |
Headlamp - Right Front Ground | -- | 1 | -- | -- |
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction |
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 5-volt reference signal to the ambient light sensor. The body control module (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 via the DRL relay control circuit. When the BCM applies ground to the DRL 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 1 and DRL 2 fuses to the left and right LO HDLP fuses to the low beam headlamps. 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. Any function or condition that turns on the headlamps will cancel DRL operation.
Headlights/Daytime Running Lights (DRL) Schematics
Exterior Lighting Systems Description and Operation
Control Module References for scan tool information
⇒ | If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction . |
⇒ | If not the specified value, refer to Brake Warning Indicator Malfunction . |
⇒ | 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. |
⇒ | 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 test lamp is always ON, test the control circuit terminal A3 X1 for a short to voltage. If the circuit tests normal, replace the underhood fuse block. |
⇒ | If the test lamp is always OFF, test the control circuit terminal A3 X1 for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block. |
• | Terminal B - with C67/C42 |
• | Terminal C - with CJ2 |
⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
⇒ | If less than the specified range, test the appropriate signal circuit terminal listed below for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
• | Terminal A - with C67/C42 |
• | Terminal D - with CJ2 |
• | Terminal A - with C67/C42 |
• | Terminal D - with CJ2 |
⇒ | 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 |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for BCM replacement, setup, and programming |