For 1990-2009 cars

### 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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Left Front Turn Signal Lamp Control | B3948 02 | B3948 04 | B3948 01 | --
Right Front Turn Signal Lamp Control | B3949 02 | B3949 04 | B3949 01 | --
Left Rear Turn Signal Lamp Control | B3950 02 | B3950 04 | B3950 01 | --
Right Rear Turn Signal Lamp Control | B3951 02 | B3951 04 | B3951 01 | --
Left Repeater Lamp Control | B3948 02 | 8 | B3948 01 | --
Right Repeater Lamp Control | B3949 02 | 9 | B3949 01 | --
Left Turn Signal Switch Signal | 2 | 2 | 2 | --
Right Turn Signal Switch Signal | 3 | 3 | 3 | --
Left Tail Lamp Ground | -- | 6 | -- | --
Left Repeater Lamp Ground | -- | 8 | -- | --
Right Repeater Lamp Ground | -- | 9 | -- | --
Right Tail Lamp Ground | -- | 7 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | --
Left Front Turn Signal Lamp Ground | -- | 4 | -- | --
Right Front Turn Signal Lamp Ground | -- | 5 | -- | --
1. All Turn Signals Lamps and/or Indicators Inoperative 2. Left Turn Signals Malfunction 3. Right Turn Signals Malfunction 4. Left Front Turn Signal Malfunction 5. Right Front Turn Signal Malfunction

6. Left Rear Turn Signal Malfunction

7. Right Rear Turn Signal Malfunction

8. Left Repeater Lamp Malfunction

9. Right Repeater Lamp Malfunction

### 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 body control module (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.

### 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, observe the scan tool Right Turn Signal Switch parameter and Left Turn Signal Switch parameter while cycling the S78 Turn Signal/Multifunction Switch between the left and right positions. The readings should toggle between ACTIVE and INACTIVE.

⇒ | If the readings do not change between the commanded states, refer to Turn Signal Switch Malfunction.

⇒ | If the readings change between the commanded states and the instrument cluster turn signal indicators are inoperative, refer to Turn Signal Indicators Malfunction.

### Circuit/System Testing

#### Turn Signal Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the S78 Turn Signal/Multifunction Switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 3.

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Left Turn Signal Switch parameter is INACTIVE.

⇒ | If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the K9 Body Control Module (BCM).

4. Verify the scan tool Right Turn Signal Switch parameter is INACTIVE.

⇒ | If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the K9 Body Control Module (BCM).

5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Left Turn Signal Switch parameter is ACTIVE.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

6. Install a 3 A fused jumper wire between the signal circuit terminal 7 and ground. Verify the scan tool Right Turn Signal Switch parameter is ACTIVE.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

7. If all circuits test normal, test or replace the S78 Turn Signal/Multifunction Switch.

#### Turn Signal Lamps Malfunction

1. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5.0 Ω between the appropriate ground circuit terminal listed below and ground.

• | E4N Park/Turn Signal Lamp - Left ground circuit terminal 2

• | E4P Park/Turn Signal Lamp - Right ground circuit terminal 2

• | E4LR Turn Signal Lamp - Left Rear ground circuit terminal 3

• | E4RR Turn Signal Lamp - Right Rear ground circuit terminal 3

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

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

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

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

• | E4N Park/Turn Signal Lamp - Left control circuit terminal 1

• | E4P Park/Turn Signal Lamp - Right control circuit terminal 1

• | E4LR Turn Signal Lamp - Left Rear control circuit terminal 2

• | E4RR Turn Signal Lamp - Right Rear control circuit terminal 2

• | E4Y Turn Signal Repeater Lamp - Left control circuit terminal 1

• | E4Z Turn Signal Repeater Lamp - Right control circuit terminal 1

4. 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.

⇒ | If the test lamp is always ON, test the control 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 control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module (BCM).

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

#### Turn Signal Indicators Malfunction

Ignition ON, command the All Indicators test ON and OFF with the scan tool, verify both turn signal indicators changes between turn ON and OFF.

⇒ | If both turn signal indicators changes between illuminate and not illuminate during the test, replace the K9 Body Control Module (BCM.

⇒ | If one or both turn signal indicators do not illuminate during the test or remain illuminated at all times, replace the P16 Instrument Cluster.

### Component Testing

#### Static Test

#### Turn Signal Switch

1. Ignition OFF, disconnect the harness connector at the S78 Turn Signal/Multifunction Switch.
2. Test for greater than 500 kΩ between signal terminal 1 and ground terminal 3.

⇒ | If less than the specified value, replace the S78 Turn Signal/Multifunction Switch.

3. Test for greater than 500 kΩ between signal terminal 7 and ground terminal 3.

⇒ | If less than the specified value, replace the S78 Turn Signal/Multifunction Switch.

4. Push the S78 Turn Signal/Multifunction Switch turn left. Test for less than 5 Ω between signal terminal 1 and ground terminal 3.

⇒ | If greater than the specified value, replace the S78 Turn Signal/Multifunction Switch.

5. Push the S78 Turn Signal/Multifunction Switch turn right. Test for less than 5 Ω between signal terminal 7 and ground terminal 3.

⇒ | If greater than the specified value, replace the S78 Turn Signal/Multifunction Switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Replacement

• | Front Side Turn Signal Lamp Replacement

• | Tail Lamp Replacement

• | Control Module References for BCM or instrument cluster replacement, setup, and programming