Circuit Description
The body control module (BCM) turns ON the automatic lighting control (ALC) headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the relay at all times through the LH HDLP fuse. The BCM grounds the ALC headlamp relay control circuit in order to activate the relay.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2575 Headlamp Control Circuit
Conditions for Running the DTC
| • | The ignition switch is in the ON position. |
| • | The ambient light sensor senses a dark condition, ALC headlamps ON. |
Conditions for Setting the DTC
The ALC headlamp relay control circuit is open for 5 seconds.
Action Taken When the DTC Sets
| • | The SERVICE indicator illuminates. |
| • | The check gages chime sounds. |
Conditions for Clearing the DTC
| • | The conditions for setting the DTC are no longer present. |
| • | A history DTC clears after 100 malfunction-free ignition cycles. |
| • | The BCM receives the clear code command from the scan tool. |
Diagnostic Aids
| • | Turn the ignition switch to the OFF position, cover the light sensor on the dash, wait for 15 seconds and then return the ignition to the ON position. The low beams should illuminate. |
| • | If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Listen for an audible click when the ALC headlamp relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
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This step tests for voltage at the coil side of the ALC headlamp relay. The LH HDLP fuse supplies power to the coil side of the ALC headlamp relay.
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This step verifies that the BCM is providing ground to the ALC headlamp relay.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Does the ALC headlamp relay turn ON and OFF with each command? | Go to Step 5 | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 9 | |
Does the test lamp turn ON and OFF with each command? | Go to Step 7 | Go to Step 6 | |
5 | Test for an open or high resistance in the low beam signal circuit and the high beam signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8 |
6 | Test for an open or high resistance in the control circuit of the ALC headlamp relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8 |
7 | Inspect for poor connections at the ALC headlamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 10 |
8 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 11 |
9 | Repair an open or high resistance in the coil side battery positive voltage circuit of the ALC headlamp relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 12 | -- |
10 | Replace the ALC headlamp relay. Did you complete the replacement? | Go to Step 12 | -- |
11 | Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming . Did you complete the replacement? | Go to Step 12 | -- |
12 |
Does the DTC reset? | Go to Step 2 | System OK |
