For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition 1 Headlight Control Module | 4 | 4 | -- | --
Ignition 2 Headlight Control Module | 5 | 5 | -- | --
Ignition Left Headlamp | 2 | 2 | -- | B1461 00
Ignition Right Headlamp | 3 | 3 | -- | B1462 00
Headlamp Leveling Sensor 5 V Reference - Front | B3415 02 | 1 | B3415 01 | --
Headlamp Leveling Sensor 5 V Reference - Rear | B3415 02 | 1 | B3415 01 | --
Headlamp Leveling Sensor Signal - Front | B3410 02 | B3410 05 | B3410 05 | B3410 08
Headlamp Leveling Sensor Signal - Rear | B3420 02 | B3420 05 | B3420 05 | B3420 08
Left Headlamp Control | B2575 00 | B2575 04 | 6 | --
Right Headlamp Control | B2699 00 | B2575 04 | 7 | --
Headlamp Leveling Sensor Low Reference - Front | -- | 1 | -- | --
Headlamp Leveling Sensor Low Reference - Rear | -- | 1 | -- | --
Left Headlamp Ground | -- | 2 | -- | B1461 00
Right Headlamp Ground | -- | 3 | -- | B1462 00
Left Cornering Lamp Ground | -- | 4 | -- | --
Right Cornering Lamp Ground | -- | 5 | -- | --

1. All Headlamp Leveling Actuator Malfunction
2. Left Headlamp Leveling Actuator Malfunction
3. Right Headlamp Leveling Actuator Malfunction
4. Left Cornering Lamp Malfunction
5. Right Cornering Lamp Malfunction
6. Left Cornering Lamp always ON
7. Right Cornering Lamp always ON

### Circuit/System Description

Battery positive voltage is applied to the headlamp control module at all times. The headlamp control module has a normal operational voltage range of about 12.5-16 V and is only fully functional with the ignition switch is in the RUN position and the headlamp switch in the AUTOMATIC LIGHT position. The communications enable signal from the body control module (BCM) wakes the headlamp control module microprocessor. The headlamp control module receives serial data messages from the engine control module (ECM), transmission control module (TCM), electronic brake control module (EBCM), and BCM with information regarding power mode, speed, steering angle, transmission gear selection, and headlamp switch status. The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a message displayed over the driver information center located on the instrument cluster.

### Reference Information

#### Schematic Reference

Headlight Leveling Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Exterior Lighting Systems Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate headlamp assembly.
2. Ignition OFF, test for less than 5 Ω between the ground circuit terminal 8 and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition OFF, test for less than 5 Ω between the ground circuit terminal 1 and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

4. Ignition ON, headlamps ON, connect a test lamp between the ignition circuit terminal 6 and ground. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

5. Ignition OFF, disconnect the X2 harness connector at the K26 Headlamp Control Module
6. Ignition ON, connect a test lamp between the ignition circuit terminal 1 (X2) at the K26 Headlamp Control Module and ground. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

7. Ignition ON, connect a test lamp between the ignition circuit terminal 2 (X2) at the K26 Headlamp Control Module and ground. The test lamp should illuminate.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

8. Reconnect the harness connector at the K26 Headlamp Control Module.
9. Ignition ON, connect a test lamp between the control circuit terminal 9 at the appropriate headlamp assembly. Command the appropriate Cornering Lamp test ON and OFF with the scan tool, verify that the test lamp changes between turn ON and OFF.

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K26 Headlamp Control Module.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K26 Headlamp Control Module.

10. If all circuits test normal, replace the appropriate headlamp assembly. Verify that the customer concern is not still present.

⇒ | If the customer concern is still present, replace the K26 Headlamp Control Module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Replacement

• | Control Module References for headlamp control module replacement, setup, and programming