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DTC B258A

DTC B258A

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 has overviews of all diagnostic categories.


DTC Descriptor

DTC B258A 01

Low Beam Control Circuit Short to Battery

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Low Beam Control

1

2

B258A 01*

-

* Right/Left Headlamp Low Beam Always ON

1. Right/Left Headlamp Low Beam Always ON

2. Right/Left Headlamp Low Beam Always OFF



Circuit/System Description

The body control module (BCM) switches the headlamp low beams ON as soon it receives a signal from the headlamp switch or ambient light sensor. When this signal is received by the BCM, it applies a voltage trough the low beam relay and the low beam supply circuits which illuminates the low beams.

Conditions for Running the DTC

The headlamp switch in OFF, AUTO or LOW BEAM position.

Conditions for Setting the DTC

The BCM detects a short to battery on the control circuit.

Action Taken When the DTC Sets

Headlamp low beam malfunction.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

Reference Information

Schematic Reference

Exterior Lights 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 information on diagnostic tools

Circuit/System Verification

Ignition ON, perform the appropriate Headlamp Low Beam Command test. The appropriate low beam lamp should be ON/OFF.

Circuit/System Testing


1. Ignition OFF, disconnect the KR49 Headlamp Low Beam Relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminals listed below and ground:

• Terminal 30

• Terminal 86

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

3. Connect a test lamp between the control circuit of KR49 Headlamp Low Beam Relay terminal 85 and B+.

4. Command the Headlamp Low Beam Command ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

5. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 Body Control Module.

6. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.

7. Remove the test lamp and reconnect the KR49 Headlamp Low Beam Relay

8. Disconnect the harness of the appropriate headlamp and connect a test lamp between the control circuit terminal 3 and ground.

9. Command the Headlamp Low Beam Command ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

10. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the KR49 Headlamp Low Beam Relay.

11. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the KR49 Headlamp Low Beam Relay.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)

• Control Module References for information on BCM replacement, setup, and programming