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 B3806 00: High Beam and Headlamp Flash Select Circuit Malfunction.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
High Beam and Headlamp Flash Select | -- | -- | -- | B3806 00

### Circuit/System Description

When the turn signal/multifunction switch is placed in the high beam or flash to pass position, the body control module (BCM) will receive a ground signal through the turn signal/multifunction switch signal circuit to illuminate the high beam lamps.

### Conditions for Running the DTC

High beam or flash activated

### Conditions for Setting the DTC

The body control module (BCM) reports stuck turn signal/multifunction switch.

### 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, turn the headlamp switch in the low beam position. Push/pull the turn signal/multifunction switch between the ON/OFF position. The high beam lamps should be ON/OFF as the switch is cycled.

### Circuit/System Testing

1. Ignition OFF, disconnect the S78 Turn Signal/Multifunction Switch harness connector. Test for less than 5 Ω between the ground circuit terminal 3 and ground.

⇒ | If greater then the specified value, test the ground circuit for an open/high resistance.

2. Connect the S78 Turn Signal/Multifunction Switch harness connector.
3. Disconnect the X3 harness connector at the K9 Body Control Module (BCM).
4. Connect a test lamp between B+ and the signal circuit terminal 17.
5. Pull the S78 Turn Signal/Multifunction Switch between the flash and OFF position. The test lamp should turn ON and OFF as the switch is cycled.

⇒ | If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

⇒ | If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

6. Push/pull the S78 Turn Signal/Multifunction Switch between the high beam and OFF position. The test lamp should turn ON and OFF as the switch is cycled.

⇒ | If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

⇒ | If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the S78 Turn Signal/Multifunction Switch.

7. If all circuits test normal, replace the K9 Body Control Module (BCM).

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the S78 Turn Signal/Multifunction Switch harness connector. S78 Turn Signal/Multifunction Switch in flash position, test for less than 5 Ω between terminal 4 and terminal 3.

⇒ | If greater than the specified value, replace the S78 Turn Signal/Multifunction Switch.

2. S78 Turn Signal/Multifunction Switch in high beam position, test for less than 5 Ω between terminal 2 and terminal 3.

⇒ | If greater than the specified value, replace the S30 Headlamp Switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

• | Turn Signal Multifunction Switch Replacement

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