For 1990-2009 cars

### Diagnostic Instructions

1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. 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
--- | --- | --- | --- | ---
Low Beam Control | B258A 02 | B258A 04 | B258A 01 | --

### Circuit/System Description

The headlamp low beam relay is supplied with battery voltage at all times. The headlamp switch signal circuit is grounded by turning the headlamp switch. The body control module (BCM) energizes the headlamp low beam relay by applying ground to the headlamp low beam relay control circuit. When the headlamp low beam relay is energized, the relay switch contacts close and battery voltage is applied through the low beam lamp fuses to the low beam lamp supply voltage circuit which illuminates the low beam lamps.

### Conditions for Running the DTC

#### B258A 01 or B258A 04

The headlamp switch in low beam position.

#### B258A 02

The headlamp switch in OFF or AUTO position.

### Conditions for Setting the DTC

#### B258A 01

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

#### B258A 02

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

#### B258A 04

The BCM detects an open control circuit.

### 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 scan tool information

### 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. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
3. 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.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 Body Control Module (BCM).

⇒ | 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 Body Control Module (BCM).

4. If all circuits test normal, test or replace the KR49 Headlamp Low Beam lamp relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

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