GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H3 🢒 Brakes 🢒 Park Brake 🢒 DTC B2602 or B2603

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

DRL Control Circuit

B2602

B2602

B2603

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Circuit/System Description

The daytime running lights (DRL) relay is controlled by the body control module (BCM). Battery positive voltage is applied to the relay coil at all times. The BCM grounds the DRL relay control circuit in order to turn ON the DRL relay illuminating the low beam headlamps at a reduced intensity.

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 stores DTC B2602 or B2603 in memory.
    • 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
    • A current DTC B2602 or B2603 clears when the BCM no longer detects an open, short to ground, or short to battery positive voltage in the control circuit on the DRL relay.
    • 100 consecutive ignition cycles have been recorded without the DTC being detected.
    • Using a scan tool can clear the DTC.

Diagnostic Aids
    • The park brake must not be set and the transmission must be is gear for the DRL to operate property.
    • 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

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, carefully supply sufficient light to the ambient light sensor to activate DRL mode. The BCM Output Data List should indicate that the DRL Status is On. The low beam headlamps should illuminate at a reduced intensity.

Circuit/System Testing
  1. Ignition OFF, disconnect the DRL relay.
  2. Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit and ground.
    3. ⇒If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance. If the voltage supply circuit fuse is open, test the relay switch control circuit for a short to ground. If the circuit tests normal, test or replace the DRL relay.
  3. Disconnect the harness connector at the BCM.
  4. Test for infinite resistance between the DRL relay control circuit and ground
    5. ⇒ If less than infinite, test the DRL relay control circuit for a short to ground.
  5. Connect the harness connector at the BCM.
  6. Connect a test lamp between the relay coil control circuit and the relay coil voltage supply circuit.
  7. Cycle the key OFF and then ON. Perform the Circuit/System Verification. The test lamp should turn ON.
    8. ⇒If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the BCM.
    ⇒If the test lamp remains ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the BCM.
  8. If all circuits test normal, test or replace the DRL relay.

Component Testing

Relay Test

  1. Ignition OFF, disconnect the DRL relay.
  2. Test for 65 to 95 ohms of resistance between terminals 85 and 86.
    3. ⇒If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 86
    • 30 and 87
    • 30 and 85
    • 85 and 87
    ⇒If less than infinite resistance, replace the relay.
  4. Test for less than 2 ohms of resistance between terminals 30 and 87A.
    5. ⇒If greater than 2 ohms, replace the relay.
  5. Install a 10-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Measure for less than 2 ohms of resistance between terminals 30 and 87.
    6. ⇒If greater than 2 ohms, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Relay Replacement
    •  Control Module References for BCM replacement, setup, and programming