B2575

DTC B2575

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Strategy Based Diagnosis
* Diagnostic Procedure Instructions

DTC Descriptor
DTC 2575 00
- Headlamp Control Circuit

Diagnostic Fault Information






Circuit/System Description

Voltage is applied at all times to the low beam headlamp relay from battery voltage. Two different inputs to the body control module (BCM) can turn ON the low beam headlamps. The headlamp switch and the ambient light sensor.

Automatic Headlamps Operation

When the ambient light sensor detects a low light condition, the BCM then applies a ground to the headlamp low beam relay control circuit. This engages the headlamp relay and applies voltage through the headlamp fuses to the low beam headlamps.

Headlamp Switch Operation

When the headlamp switch is placed in the ON position, ground is applied to the BCM through the headlamp switch circuit. The BCM then applies a ground to the headlamp low beam relay control circuit. This engages the headlamp relay and applies voltage through the headlamp fuses to the low beam headlamps.

Conditions for Running the DTC

The ignition is ON. The headlamps must be commanded ON by either the BCM or by the headlamp switch.

Conditions for Setting the DTC

The BCM detects a short to voltage on the low beam headlamps relay control circuit while trying to apply a ground to the circuit.

Action Taken When the DTC Sets

The low beam headlamps are not illuminated.

Conditions for Clearing the DTC

The BCM clears this code from current when the fault is removed from the system.

Circuit/System Verification

Ignition ON, turn the headlamps ON. The headlamps should illuminate.

Circuit/System Testing

1. Ignition ON, automatic head lights OFF, verify the scan tool LO BEAM relay command parameter displays ON with the head lamp switch in the ON position.

• If the scan tool displays OFF, test the head lamp switch head lamps ON signal circuit terminal 1 and head lamp switch ground circuit terminal 8 for a short to voltage or an open/high resistance. If the circuits test normal, replace the head light switch.

2. Ignition OFF, disconnect the LOW BEAM relay.
3. Verify that a test lamp illuminates between the B+ circuit on the coil side and switch side of the relay terminals when connected to ground.

• 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 left and right low beam supply voltage circuits for a short to ground. If the circuits test normal replace the appropriate head lamp assembly.

4. Disconnect the harness connector at an inoperative head lamp assembly.
5. Test for less than 1.0 ohm of resistance between the inoperative head lamp ground circuit terminal F and ground.

• If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

6. Connect the harness connector at the head lamp.
7. Connect a 30-amp fused jumper wire between the B+ circuit terminal and the appropriate head lamp supply voltage circuit terminal of the low beam head lamp relay. Verify the head lamps illuminate.

• If the head lamps do not illuminate, test the left and right head lamp supply voltage circuits for an open/high resistance. If the circuits test normal, replace the inoperative head lamp assembly.

8. Connect a test lamp between the B+ circuit terminal of the relay and the Low Beam relay control circuit terminal.
9. Command the LO BEAM relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always OFF, test the low beam relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the Body Control Module.

10. If all circuits test normal, replace the LO BEAM relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Programming and Relearning for BCM setup, and programming. Programming and Relearning