Circuit Description
The body control module (BCM) turns on the headlamp relay when the ambient light sensor senses a dark condition. Battery positive voltage is supplied to the headlamp relay at all times through the BACKUP/TURN fuse. The BCM grounds the headlamp relay control circuit in order to activate the relay.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2577 Headlamp Relay Output Circuit Low
Conditions for Running the DTC
| • | The ignition switch is in the ON position. |
| • | The ambient light sensor senses a light condition (automatic lamp control (ALC) headlamps off). |
Conditions for Setting the DTC
Either of the following conditions will set this DTC:
| • | The headlamp relay control circuit is open for 5 seconds. |
| • | The headlamp relay control circuit is shorted to ground for 5 seconds. |
Action Taken When the DTC Sets
The SERVICE indicator will illuminate.
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
| • | If the headlamp relay control circuit is open, the ALC headlamps will be inoperative. |
| • | In the headlamp relay control circuit is shorted to ground, the ALC headlamps will be always on. |
| • | If the DTC is a history DTC, the problem may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . |
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 headlamp relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
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Tests for voltage at the coil side of the headlamp relay. The BACKUP/TURN fuse supplies battery positive voltage to the coil side of the headlamp relay.
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Verifies that the BCM is providing ground to the headlamp relay.
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Tests if ground is constantly being applied to the headlamp relay.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
Does the headlamp relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 10 | |
Does the test lamp turn ON and OFF with each command? | Go to Step 8 | Go to Step 5 | |
Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 6 | |
6 | Test the control circuit of the headlamp relay for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
7 | Test the control circuit of the headlamp relay for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
8 | Inspect for poor connections at the headlamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
9 | 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 . Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
10 | Repair the coil side battery positive voltage circuit of the headlamp relay. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 13 | -- |
11 | Replace the headlamp relay. Refer to Relay Replacement . Did you complete the replacement? | Go to Step 13 | -- |
12 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 13 | -- |
13 |
Does the DTC reset? | Go to Step 2 | System OK |
