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DTC B3806

DTC B3806

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 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
Headlamp High Beam Signal B3650 08 1 1 -
Headlamp Flash To Pass Signal B3806 00 2 2 -
Turn Signal/Multifunction Switch Ground - 1, 2 - -
1. Headlamp Dimmer Switch Malfunction 2. Headlamp Flash To Pass Switch Malfunction


Circuit/System Description

The BCM monitors the voltage level within the high beam signal circuit and the flash to pass signal circuit. When the turn signal/multifunction switch is moved to the high beam position or to the flash to pass position, the voltage within the appropriate signal circuit drops to less than 1 V. The BCM will detect the voltage drop and will command the headlamp high beams to turn ON or OFF.

Conditions for Running the DTC

Battery voltage must be between 9-16 V.

Conditions for Setting the DTC

The BCM detects a short to ground in the headlamp flash to pass signal circuit for greater than 15 seconds.

Action Taken When the DTC Sets

The high beam headlamps will malfunction.

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, observe the scan tool Headlamps Flash Switch parameter while pulling and releasing the turn signal/multi-function switch. The value should change between Inactive and Active when changing between the selected states.

Circuit/System Testing


1. Ignition OFF, disconnect at the S78 turn signal/multifunction switch.

2. Ignition ON, verify that the scan tool Headlamps Flash Switch parameter is Inactive.

3. If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K9 BCM.

4. Connect a 3 A fused jumper wire between the signal circuit terminal 4 and ground. Verify that the scan tool Headlamps Flash Switch parameter is Active.

5. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

6. If all circuits test normal, test or replace the S78 turn signal/multifunction switch.


Component Testing


Turn Signal/Multifunction Switch Test

1. Ignition OFF, disconnect the harness connector at the S78 turn signal/multifunction switch.

2. Test for Infinite resistance between the terminals listed below with the switch in the open position.

• Signal terminal 2 and ground terminal 3

• Signal terminal 4 and ground terminal 3

3. If not the specified value, replace the S78 turn signal/multifunction switch.

4. Test for less than 2 Ω between the signal terminal 2 and the ground terminal 3 with the switch in the high beam position.

5. If greater than the specified value, replace the S78 turn signal/multifunction switch.

6. Test for less than 2 Ω between the signal terminal 4 and the ground terminal 3 while holding the switch in the flash to pass position.

7. If greater than the specified value, replace the S78 turn signal/multifunction switch.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Turn Signal Multifunction Switch Replacement

• Control Module References for BCM replacement, programming and setup