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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 provides an overview of each diagnostic category.


DTC Descriptor

DTC B258A 01

Low Beam Control Circuit Short to Battery

DTC B258A 02

Low Beam Control Circuit Short to Ground

DTC B258A 04

Low Beam Control Circuit Open

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Headlamp Low Beam Relay Control B258A 02 B258A 04 B258A 01 -


Circuit/System Description

When the headlight switch is placed in low beam position, the body control module (BCM) energizes the low beam headlamp relay which supplies battery voltage to the respective headlamp control circuits.

Conditions for Running the DTC

The headlamp switch is in the low beam position.

Conditions for Setting the DTC

B258A 01

The BCM detects a short to voltage in the headlamp low beam relay control circuit.

B258A 02

The BCM detects a short to ground in the headlamp low beam relay control circuit.

B258A 04

The BCM detects an open/high resistance in the headlamp low beam relay control circuit.

Action Taken When the DTC Sets

B258A 01 or B258A 04

The low beam headlamps will be inoperative.

B258A 02

The low beam headlamps will be continuously illuminated.

Conditions for Clearing the DTC


• The DTC will be current for as long as the fault is present.

• When the fault is no longer present, the DTC will be a history DTC.

• A history DTC will clear after 50 ignition cycles.


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, command the Headlamp Low Beam ON and OFF with a scan tool. The low beam lamp should turn ON and OFF when changing between the commanded states.

Circuit/System Testing


1. Ignition OFF, disconnect the KR49 headlamp low beam relay.

2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 30 and ground.

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

4. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.

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

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

7. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

8. Connect a 15A fused jumper wire between the B+ circuit terminal 87 and the control circuit terminal 30. Verify the E4G headlamp-left low beam and the E4H headlamp-right low beam are activated.

9. If the E4G headlamp-left low beam and the E4H headlamp-right low beam do not activate, test the control circuit for a short to ground or an open/high resistance.

10. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.

11. Ignition ON, command the low beam lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

12. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM.

13. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

14. If all circuits test normal, test or replace the KR49 headlamp low beam relay.


Component Testing


Relay Test

1. Ignition OFF, disconnect the KR49 headlamp low beam relay.

2. Test for 60-180 Ω between terminals 85 and 86.

3. If not within the specified range, replace the KR49 headlamp low beam relay.

4. Test for infinite resistance between the following terminals:

• 30 and 86

• 30 and 87

• 30 and 85

• 85 and 87

5. If not the specified value, replace the KR49 headlamp low beam relay.

6. Install a 15A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

7. If greater than the specified range, 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 BCM replacement, setup, and programming