B3909

DTC B3909

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC B3909 05
- Low Beam Switch Circuit Open or High Voltage




Diagnostic Fault Information






Circuit/System Description

The headlamp switch is supplied with voltage from the instrument panel cluster (IPC) by two signal circuits, the headlamp signal circuit and the park lamp signal circuit. When the headlamp switch is placed in either the AUTO or HEAD position, the headlamps signal circuit is provided with ground through the switch contacts of the headlamp switch to a common headlamp switch ground back to the IPC. The IPC interprets the flow of voltage and responds by sending a serial data message to the underhood electrical center (UEC) requesting the headlamps be activated. The UEC responds by applying voltage to the left and right headlamp control circuits illuminating the headlamps. Ground for the left headlamp is supplied at G101 and the right headlamp receives ground at G102.


Conditions for Running the DTC

* Battery voltage must be between 9-16 volts.
* AUTO headlamp ON.



Conditions for Setting the DTC

The DTC will set when the IPC detects a short to voltage or an open/high resistance in the headlamp switch AUTO signal circuit.


Actions Taken When the DTC Sets

When DTC B3909 05 is present, the AUTO headlamp signal circuit will be disabled.


Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, verify a test lamp illuminates between B+ and the ground circuit terminal 11.

• If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

3. Ignition ON, verify the scan tool Auto Headlamp Drive parameter is OFF.

• If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the IPC.

4. Install a 3A fused jumper wire between the signal circuit terminal 5 and ground. Verify the scan tool Auto Headlamp Drive parameter is ON.

• 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 IPC.

5. If all circuits test normal, replace the headlamp switch.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Headlamp Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for IPC replacement, setup, and programming