Buick Regal: DTC B3948 or B3949

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 Descriptors

DTC B3948 01

Left Front Turn Signal Circuit Short to Battery

DTC B3948 02

Left Front Turn Signal Circuit Short to Ground

DTC B3948 04

Left Front Turn Signal Circuit Open

DTC B3949 01

Right Front Turn Signal Circuit Short to Battery

DTC B3949 02

Right Front Turn Signal Circuit Short to Ground

DTC B3949 04

Right Front 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 front/side and rear turn signal lamps through their respective voltage supply circuits.

Conditions for Running the DTC

B3948 01 and B3949 01

The appropriate turn signal is inactive

B3948 02, B3948 04, B3949 02 and B3949 04

The appropriate turn signal is active

Conditions for Setting the DTC

B3948 01 and B3949 01

The BCM detects a short to voltage on the control circuit.

B3948 02 and B3949 02

The BCM detects a short to ground on the control circuit.

B3948 04 and B3949 04

The BCM detects an open 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 Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

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, perform the Left Front Turn Signal Lamp test. The left front turn signal lamp, turn signal repeater light and outside wing mirror light should be ON/OFF.

Perform the Right Front Turn Signal Lamp test. The right front turn signal lamp, turn signal repeater light and outside wing mirror light should be ON/OFF.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp.

2. Test for less than 5 Ω between the appropriate turn signal lamp ground circuit harness connector listed below and ground.

• E13RA Headlamp Assembly - Right ground circuit harness connector terminal 1
• E13LA Headlamp Assembly - Left ground circuit harness connector terminal 1
• A9A Outside Rearview Mirror - Driver ground circuit harness connector terminal 5
• A9B Outside Rearview Mirror - Passenger ground circuit harness connector terminal 5
• If greater than the specified value, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the appropriate turn signal lamp control circuit harness connector listed below and ground.

• E13RA Headlamp Assembly - Right ground circuit harness connector terminal 5
• E13LA Headlamp Assembly - Left ground circuit harness connector terminal 5
• A9A Outside Rearview Mirror - Driver ground circuit harness connector terminal 13
• A9B Outside Rearview Mirror - Passenger ground circuit harness connector terminal 13

4. Command the appropriate turn signal lamp test 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 Body Control Module.
• 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 Body Control Module.

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Headlamp Replacement
• Outside Rearview Mirror Replacement
• Front Side Turn Signal Lamp Replacement
• Control Module References for BCM replacement, setup and programming

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