For 1990-2009 cars

### 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 Descriptors

DTC B3950 01: Left Rear Turn Signal Circuit Short to Battery
DTC B3950 02: Left Rear Turn Signal Circuit Short to Ground
DTC B3950 04: Left Rear Turn Signal Circuit Open
DTC B3951 01: Right Rear Turn Signal Circuit Short to Battery
DTC B3951 02: Right Rear Turn Signal Circuit Short to Ground
DTC B3951 04: Right Rear Turn Signal Circuit Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Left Rear Turn Signal | B3950 02 | B3950 04 | B3950 01 | --
Right Rear Turn Signal | B3951 02 | B3951 04 | B3951 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 right turn or left turn signal switch signal circuit to the body control module (BCM) and the trailing lighting converter. The BCM and the trailing lighting converter then applies a voltage to the rear turn signal lamps through there respective voltage supply circuits.

### Conditions for Running the DTC

#### B3950 01 and B3951 01

The appropriate turn signal is inactive.

#### B3950 02, B3950 04, B3951 02 or B3951 04

The appropriate turn signal is active.

### Conditions for Setting the DTC

#### B3950 01 or B3951 01

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

#### B3950 02 or B3951 02

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

#### B3950 04 or B3951 04

The control module detects an open control circuit.

### Action Taken When the DTC Sets

The appropriate turn signal is inoperative.

### Conditions for Clearing the DTC

The condition for setting the DTC is not 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

• | 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 appropriate Rear Turn Signal/Hazard Lamp Command test. The appropriate rear turn signal/hazard lamp should be ON/OFF

### Circuit/System Testing

1. Ignition OFF, disconnect the appropriate harness connector at the tail lamp listed below:

• | E4LR Turn Signal Lamp - Left Rear

• | E4RR Turn Signal Lamp - Right Rear

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

• | E4LR Turn Signal Lamp - Left Rear harness connector terminal 3

• | E4RR Turn Signal Lamp - Right Rear harness connector terminal 3

⇒ | 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.

• | E4LR Turn Signal Lamp - Left Rear harness connector terminal 2

• | E4RR Turn Signal Lamp - Right Rear harness connector terminal 2

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 appropriate 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 appropriate control module.

5. If all the circuits test normal, replace the appropriate tail lamp/liftgate tail lamp.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Replacement

• | Control Module References for BCM or trailer lighting converter replacement, setup and programming