B3951

DTC B3950 or B3951

Diagnostic Instructions

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

DTC Descriptors
DTC B3950 02
- Left Rear Turn Signal Circuit Short to Ground

DTC B3950 04
- Left Rear Turn Signal Circuit Open

DTC B3951 02
- Right Rear Turn Signal Circuit Short to Ground

DTC B3951 04
- Right Rear Turn Signal Circuit Open

Diagnostic Fault Information





Circuit/System Description

Ground is applied at all times to the turn signal/multifunction switch. When the turn signal/multifunction switch is placed in either the turn right or turn left position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM then applies a voltage to the rear turn signal lamps through their respective voltage supply circuits.

Conditions for Running the DTC

The appropriate rear turn signal is active.

Conditions for Setting the DTC

B3950 02 or B3951 02

The BCM detects a short to ground on the appropriate rear turn signal control circuit.

B3950 04 or B3951 04

The BCM detects an open circuit on the appropriate rear turn signal control circuit.

Action Taken When the DTC Sets

The appropriate turn signal lamp is inoperative.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights 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 (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

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

Circuit/System Verification

Ignition ON, command the appropriate Rear Turn Signal Lamp ON and OFF with a scan tool. The appropriate rear turn signal lamp should turn ON and OFF when changing between the commanded states.

Circuit/System Testing

Note: If DTC B3950 02 or B3951 02 are set fuse block underhood BCM fuse 32 may be open. Test circuit and fuse before replacing BCM.

1. Ignition OFF, disconnect the harness connector at the appropriate E42 tail lamp assembly.
2. Test for less than 5 ohm between the ground circuit terminal C and ground.

• If greater than the specified value, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal E and ground.
4. Command the appropriate Rear Turn Signal Lamp 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 signal circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.
• If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the K9 BCM.

5. If all the circuits test normal, replace the E42 tail lamp assembly.

Repair Instructions

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

* Tail Lamp Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup and programming