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DTC B3948 or B3949

DTC B3948 or B3949

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 B3948 02

Left Front Turn Signal Circuit Short to Ground

DTC B3949 02

Right Front Turn Signal Circuit Short to Ground

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Left Front Turn Signal Lamp Control B3948 02 1 2 -
Right Front Turn Signal Lamp Control B3949 02 1 2 -
Left Repeater Lamp Control B3948 02 1 2 -
Right Repeater Lamp Control B3949 02 1 2 -
Left Tail Lamp Ground - 1 - -
Right Tail Lamp Ground - 1 - -
1. Turn Signal Lamps Inoperative 2. Turn Signal Lamps Always ON


Circuit/System Description

Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the BCM through either the right turn or left turn signal switch signal circuit. The BCM then applies a pulsating voltage to the front and rear turn signal lamps through there respective voltage supply circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument cluster requesting the respective turn signal indicator be pulsed ON and OFF.

Conditions for Running the DTC

When the appropriate turn signal is commanded

Conditions for Setting the DTC

B3948 02

The BCM detects a short to ground on the left front turn signal control circuit.

B3949 02

The BCM detects a short to ground on the right front turn signal control circuit.

Action Taken When the DTC Sets

The appropriate turn signal lamp is inoperative.

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

Exterior Lights 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


1. Ignition ON, with the turn signal switch in the left position, observe the function of the E4LF turn signal lamp-left front and the E4Y turn signal repeater lamp-left. Each lamp should flash ON and OFF.

2. With the turn signal switch in the right position, observe the function of the E4RF turn signal lamp-right front and the E4Z turn signal repeater lamp-right. Each lamp should flash ON and OFF.


Circuit/System Testing


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

2. Test for less than 30 Ω between the ground circuit terminal listed below and ground.

• E4Y turn signal repeater lamp-left terminal 2

• E4Z turn signal repeater lamp-right terminal 2

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

4. Disconnect the inline harness connector at the appropriate E4LF turn signal lamp-front listed below:

• E4LF turn signal lamp-left front X115 (Without TT6/TT7/TT8)

• E4LF turn signal lamp-left front X111 (With TT6/TT7/TT8)

• E4RF turn signal lamp-right front X116 (Without TT6/TT7/TT8)

• E4RF turn signal lamp-right front X112 (With TT6/TT7/TT8)

5. Connect a test lamp between the control circuit terminal listed below and ground.

• E4LF turn signal lamp-left front terminal J

• E4RF turn signal lamp-right front terminal J

• E4Y turn signal repeater lamp-left terminal 1

• E4Z turn signal repeater lamp-right terminal 1

6. Command the appropriate Turn Signal Lamp ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

7. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.

8. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 BCM.

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


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Front Turn Signal Lamp Bulb Replacement (TT6 Right Hand Bulb) Front Turn Signal Lamp Bulb Replacement (TT6 Left Hand Bulb)

• Control Module References for BCM replacement, setup, and programming