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B2575



DTC B2575

DTC DESCRIPTOR

DTC B2575
Headlamp Control Circuit

DIAGNOSTIC FAULT INFORMATION




Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure Initial Inspection and Diagnostic Overview.

CIRCUIT/SYSTEM DESCRIPTION
The body control module (BCM) grounds the headlamp relay control circuit when the ambient light sensor senses a dark condition. Voltage is supplied to the headlamp relay when the ignition is on the RUN position.

CONDITIONS FOR RUNNING THE DTC
- The ignition switch is in the RUN position.
- The ambient light sensor senses a dark condition.
- The headlamp switch is in the AUTO position.
- Transmission gear selectors not in the PARK position.

CONDITIONS FOR SETTING THE DTC
- The headlamp relay control circuit is open for 5 seconds.
- The headlamp relay coil is open.
- Ignition voltage to the headlamp relay is open.
- The low bean signal circuit is open between the headlamp switch and the instrument panel (I/P) fuse block.
- The headlamp relay output circuit is open.
- The ground is open to the headlamp relay switch.

ACTION TAKEN WHEN THE DTC SETS
The headlamps will not illuminate in the AUTO position.

CONDITIONS FOR CLEARING THE DTC
- A current DTC will clear when the conditions for setting the DTC are no longer present.
- 100 consecutive ignition cycles have been recorded without the DTC being detected.
- Using a scan tool can clear the DTC.

DIAGNOSTIC AIDS
- Turn the ignition switch to the OFF position, cover the ambient light sensor on the instrument panel, wait for 15 seconds and then return the ignition to the ON position. The headlamps should illuminate.
- An open in the following circuits may cause DTC B2575
- Low beam signal circuit
- Headlamp relay output circuit
- Ground to the headlamp switch or relay

CIRCUIT/SYSTEM VERIFICATION
Ignition ON, observe the scan tool high beam switch while turning the headlamp switch. The reading should change between OFF and ON.

CIRCUIT/SYSTEM TESTING

High Beam or Low Beam Circuit Testing
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition ON, verify that a test lamp illuminates between the voltage supply circuit and ground.
- If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, also test the signal circuit for a short to ground.
3. Verify the scan tool high beam switch is OFF.
- If not OFF, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.
4. Install a 3-amp fused jumper wire between the voltage supply circuit and ground. Verify the scan tool high beam switch is ON.
- If not ON, test the signal circuit for an open/high resistance or a short to voltage. If circuit tests normal, replace the BCM.
5. If all circuits test normal, test or replace the headlamp switch.

Headlamp Relay Testing
1. Ignition OFF, disconnect the headlamp relay.
2. Ignition ON, verify the headlamps are deactivated.
- If the headlamps are still activated, repair the relay switch control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the relay coil voltage supply circuit and ground.
- If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, test or replace the relay.
4. Verify that a test lamp illuminates between the relay switch voltage supply circuit and ground.
- If the test lamp does not illuminate, repair the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the relay switch voltage supply circuit fuse is open, test the relay switch control circuit for a short to ground.
5. Test for less than 1 ohm of resistance between the relay switch circuit ground and ground
- If greater than 1 ohm, test the ground circuit for an open/high resistance
6. Connect a 15-amp fused jumper wire between the relay switch voltage supply circuit and the relay switch control circuit. Verify the headlamps are activated.
- If the headlamps are not activated, test the relay switch control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp switch.
7. Connect a test lamp between the relay coil control circuit and the relay coil voltage supply circuit.
8. Command the headlamp relay ON and OFF by placing the headlamp switch in the AUTO position and covering and uncovering the ambient light sensor. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp remains ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the BCM.
- If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the BCM.
9. If all circuits test normal, test or replace the headlamp relay.

COMPONENT TESTING

Headlamp Switch Testing
1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal terminal and the voltage supply terminal with the switch in the open position.
- If less than infinite resistance, replace the headlamp switch.
3. Test for less than 1.5 ohms between the signal terminal and the voltage supply terminal with the switch in the closed position.
- If greater than 1.5 ohms, replace the headlamp switch.

Relay Testing
1. Ignition OFF, disconnect the headlamp relay.
2. Test for 65 to 95 ohms of resistance between terminals 85 and 86.
- If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals:
- 30 and 86
- 30 and 87
- 30 and 85
- 85 and 87
- If less than infinite resistance, replace the relay.
4. Test for less than 2 ohms of resistance between terminals 30 and 87A.
- If greater than 2 ohms, replace the relay.
5. Install a 15-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Measure for less than 2 ohms of resistance between terminals 30 and 87.
- If greater than 2 ohms, replace the relay.

REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the diagnostic procedure Verification Tests.
Control Module References for BCM replacement, setup and programming Programming and Relearning
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