Diagnostic Instructions

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

DTC Descriptor

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	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Left Front Turn Signal	B3948 02	B3948 04	B3948 01	--
Right Front Turn Signal	B3949 02	B3949 04	B3949 01	--

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.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

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

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

Ignition ON, 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.

•	E3RH Right Front Turn Signal Lamp ground circuit harness connector terminal 1

•	E4Z Turn Signal Repeater Lamp - Right ground circuit harness connector terminal 2

•	E3LH Left Front Turn Signal Lamp ground circuit harness connector terminal 1

•	E4Y Turn Signal Repeater Lamp - Left ground circuit harness connector terminal 2

•	A9A Outside Rearview Mirror - Driver ground circuit harness connector terminal 4

•	A9B Outside Rearview Mirror - Passenger ground circuit harness connector terminal 4

⇒	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.

•	E3RH Right Front Turn Signal Lamp circuit harness connector terminal 5

•	E4Z Turn Signal Repeater Lamp - Right circuit harness connector terminal 1

•	E3LH Left Front Turn Signal Lamp circuit harness connector terminal 5

•	E4Y Turn Signal Repeater Lamp - Left circuit harness connector terminal 1

•	A9A Outside Rearview Mirror - Driver ground circuit harness connector terminal 16

•	A9B Outside Rearview Mirror - Passenger ground circuit harness connector terminal 16

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 (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 Body Control Module (BCM).

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.