Circuit Description
When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The headlamp low beam relay will apply voltage to illuminate the headlamps.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2575 Headlamp Control Circuit
Conditions for Running the DTC
The battery voltage must be between 9-16 volts.
Conditions for Setting the DTC
| • | When the low beam headlamp relay control circuit is open or shorted to ground |
| • | When the BCM receives a low beam headlamp ON command and the low beam headlamp relay control circuit is shorted to voltage. |
| • | When the low beam relay coil side is open or the battery positive voltage to the low beam relay is open |
Action Taken When the DTC Sets
The low beam headlamps will not operate or will remain always on.
Conditions for Clearing the MIL/DTC
| • | This DTC will clear on current status after the condition for setting the fault is corrected. |
| • | A history DTC will clear after 100 consecutive ignition cycles without a fault present. |
| • | History and current DTCs can be cleared using a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests for voltage at the voltage supply side of the headlamp low beam relay.
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This step verifies that the BCM is providing ground to the headlamp low beam relay.
-
This step tests if ground is constantly being applied to the headlamp low beam relay.
-
This step tests if there is opposing voltage present or an open headlamp low beam relay control circuit.
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After replacement of the BCM, you must calibrate the new module for proper operation.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Headlights Schematics Connector End View Reference: Lighting Systems Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Do the low beam headlamps turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | 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 | |
Test the control circuit of the headlamp low beam relay for a short to battery positive voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 | |
7 | Test the control circuit of the headlamp low beam relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
8 | Inspect for poor connections at the headlamp low beam relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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 Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
10 | Repair the poor connection or an open in the battery positive voltage circuit of the headlamp low beam relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
11 | Replace the headlamp low beam relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | Go to Step 13 | -- |
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 13 | -- | |
13 |
Does the DTC reset? | Go to Step 2 | System OK |
