B2602
DTC B2602 or B2603
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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/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 Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Component Connector End Views Connector End Views By Name
Description and Operation
Exterior Lighting Systems Description and Operation Exterior Lighting Systems
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References 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 86 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 30 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 or RF Turn Lamp/DRL ON and OFF with 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 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 Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Control Module References Control Module References for BCM replacement, setup, and programming