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.

### DTC Descriptor

DTC B2600: Daytime Running Lamp Control Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Battery Positive Voltage Circuit to the Headlamp | B2600 | B2600 | -- | --
DRL Resistor Ground Circuit | -- | B2600 | B2600 | --
DRL Relay Control Circuit | B2600 | B2600 | -- | --
DRL Relay | B2600 | B2600 | B2600 | --
BCM | B2600 | B2600 | -- | --

### Circuit/System Description

The daytime running lamps (DRL) are controlled by the body control module (BCM). The BCM grounds the DRL relay control circuit in order to energize the DRL relay coil. This action places the right and left headlamps in series with each other with the DRL relay providing the ground path and the RT HDLP fuse providing battery positive voltage. The BCM monitors the low and high beam circuits to ensure that the DRLs are operating properly. If the BCM senses that the DRLs are not operating properly, DTC B2600 is set.

### Conditions for Running the DTC

• | The ignition switch is in the RUN position.

• | The headlamp switch is in the AUTO position.

• | The park brake is not applied.

• | The gear selector is not in the PARK position.

### Conditions for Setting the DTC

• | The DRL resistor supply voltage circuit is open, or shorted to ground.

• | The headlamp low beam signal circuit between a headlamp and the Underhood fuse block is open or shorted to ground.

• | The battery positive voltage circuit to the headlamp is open or shorted to ground.

• | One of the headlamp fuses in the Underhood fuse block are open.

• | The DRL resistor ground circuit is open.

• | The DRL resistor is open or shorted.

• | The DRL relay is stuck in the OPEN position.

### Action Taken When the DTC Sets

The BCM turns off the DRL relay control for the remainder of the ignition cycle.

### Conditions for Clearing the DTC

• | A current DTC B2600 clears when the BCM no longer detects a short to battery positive voltage in the control circuit on the park lamp relay.

• | 100 consecutive ignition cycles have been recorded without the DTC being detected.

• | Using a scan tool can clear the DTC.

### Diagnostic Aids

• | Check both the LH and RH headlamps for proper operation

• | Check both the LH High Beam, LH Low Beam and RH High Beam and RH Low Beam Head lamp fuses located in the underhood fuseblock.

• | If DTC B2602 also sets, perform the diagnostics for DTC B2602 before performing diagnostics for DTC B2600

### Reference Information

#### Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

#### Connector End View Reference

Lighting Systems Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data Definitions

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Verification

Ignition ON, command the DRL ON and OFF with a scan tool, observe the DRL. The DRLs should turn ON and OFF with each command.

### Circuit/System Testing

1. Ignition OFF, disconnect the C2 DRL harness connector at the BEC.
2. Connect a test lamp between the control circuit terminal 38 and B+.
3. Command the DRL 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Ignition OFF, connect the C2 DRL harness connector at the BEC. Disconnect the harness connector at the inoperative low beam head lamps.
5. Test for less than 1.0 ohm of resistance between the appropriate head lamp ground circuit terminal 2 and ground.

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

6. Connect a test lamp between the control circuit terminal 1 and ground.
7. Command the DRL 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 ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BEC.

⇒ | If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the BEC.

⇒ | If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the appropriate head lamp.

8. If all circuits test normal, replace the appropriate head lamp.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure

• | Headlamp Replacement

• | Control Module References for BCM replacement, setup, and programming

• | Underhood Electrical Center or Junction Block Replacement