B3951

DTC B3948-B3951

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 Descriptors
DTC B3948
- Left Front Turn Signal

DTC B3949
- Right Front Turn Signal

DTC B3950
- Left Rear Turn Signal

DTC B3951
- Right Rear Turn Signal

Diagnostic Fault Information





Circuit/System Description

The Body Control Module (BCM) controls the turn signals based on an input from the turn signal switch, part of the multifunction turn signal lever. The BCM receives an input from one of two signal circuits to determine which turn signal function is requested. When the turn signal lever is placed in the LEFT position, the left turn signal switch signal circuit is grounded indicating that left turn signal operation is requested. When the turn signal lever is placed in the RIGHT position, the right turn signal switch signal circuit is grounded indicating that right turn signal operation is requested.

When a turn signal input is received from the turn signal switch, the BCM will activate the appropriate turn signals. The BCM pulses voltage to the applicable turn signals via the turn signal lamp supply voltage circuits, illuminating the required turn signal lamps.

Conditions for Running the DTC

A turn signal input is received from the turn signal switch.

Conditions for Setting the DTC

B3948

A short to voltage, short to ground, or an open/high resistance is seen on the left front turn signal lamp supply voltage circuit.

B3949

A short to voltage, short to ground, or an open/high resistance is seen on the right front turn signal lamp supply voltage circuit.

B3950

A short to voltage, short to ground, or an open/high resistance is seen on the left rear stop/turn signal lamp supply voltage circuit.

B3951

A short to voltage, short to ground, or an open/high resistance is seen on the right rear stop/turn signal lamp supply voltage circuit.

Action Taken When the DTC Sets

The applicable turn signal is 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

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 (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 Verification

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

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp bulb.
2. Test for less than 10 ohms between the ground circuit terminal G (Rear) or C (Front) and ground.

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

3. Install a test lamp between the signal circuit terminal A and ground.
4. Ignition ON, command the appropriate turn signal lamp ON and OFF with a scan tool. The appropriate turn signal 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 BCM.
• If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the appropriate turn signal lamp bulb.

Repair Instructions

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

* Parking and Turn Signal Lamp Bulb Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming