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 Descriptors

DTC B2602: Daytime Running Lamp Control Circuit Low or Open
DTC B2603: Daytime Running Lamp Control Circuit High

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Light Sensor Signal | B2647 00 | B2648 00 | B2648 00 | --
Ambient Light Sensor Low Reference | -- | 2 | 2 | --
Daytime Running Lamp Relay Control | B2602 00 | B2602 00 | B2603 00 | --
Daytime Running Lamp - Left Voltage Supply | 2 | 2 | 2 | --
Daytime Running Lamp - Right Voltage Supply | 2 | 2 | 2 | --
Headlamp - Left Front Low Beam Supply Voltage | 1 | 1 | 1 | --
Headlamp - Right Front Low Beam Supply Voltage | 1 | 1 | 1 | --
Daytime Running Lamp - Left Ground | -- | 2 | -- | --
Daytime Running Lamp - Right Ground | -- | 2 | -- | --
Headlamp - Left Front Ground | -- | 1 | -- | --
Headlamp - Right Front Ground | -- | 1 | -- | --

1. Headlamps Malfunction
2. Daytime Running Lamps Malfunction

### Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

### 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

One of the following conditions must occur:

• | The DRL relay control circuit is open, shorted to ground, or shorted to voltage.

• | The DRL relay coil is open.

• | The battery positive voltage to the DRL relay is open.

### Action Taken When the DTC Sets

• | The BCM disables the DRL relay control as long as the fault is present.

• | The BCM disables the DRL relay control until the next key cycle after the fault is corrected.

### 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.

### Diagnostic Aids

• | The park brake must not be set and the transmission must be is gear for the DRL to operate properly.

• | An open, short to ground, or a short to voltage in the following location may cause a malfunction to occur:

- | The control circuit of the DRL relay coil

- | The DRL relay

- | The BCM

### 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 Testing

1. Ignition OFF, disconnect the DRL relay.
2. Ignition ON, verify a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify a test lamp illuminates between the B+ circuit terminal 30 and 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 control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the DRL relay.

4. Verify a test lamp illuminates between the B+ circuit terminal 86 and ground.

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

5. Connect a test lamp between the relay control circuit terminal 85 and the B+ circuit terminal 86. Command the LF and RF Turn Lamp/DRL ON and OFF with scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒ | If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the BCM.

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

6. If all circuits test normal, replace the DRL relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

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