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 00: Daytime Running Lamp Control Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Light Sensor Signal | B2645 03 | B2645 07 | B2645 07 | --
DRL Relay Control | 1 | 1 | B2600 00 | --
Ambient Light Sensor Ground | -- | B2645 07 | -- | --
1. Daytime Running Lamps Malfunction

### Circuit/System Description

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs ON by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL 1 and DRL 2 fuses to the left and right LO BEAM fuses to the low beam headlamps. Any function or condition that turns on the headlamps will cancel DRL operation.

### Conditions for Running the DTC

• | Battery voltage must be between 9-16 volts.

• | Headlamp switch in AUTO position.

### Conditions for Setting the DTC

DTC B2600 00 will set when the BCM detects a short to voltage in the DRL relay control circuit.

### Actions Taken When the DTC Sets

The BCM will disable the DRL relay control circuit.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

Headlights/Daytime Running Lights (DRL) 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 Verification

Ignition ON, verify with a scan tool the park brake switch parameter displays Released.

⇒ | If not the specified value, refer to Brake Warning Indicator Malfunction.

### Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
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 open/high resistance. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, replace the underhood fuse block.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure

• | Underhood Electrical Center or Junction Block Replacement

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