GM Service Manual Online
For 1990-2009 cars only

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

Hazard Switch Signal

2

2

2

--

Left Turn Signal Switch Signal

3

3

3

--

Right Turn Signal Switch Signal

3

3

3

--

Left Front Turn Signal Lamp Control

B3948 02

B3948 05

B3948 05

--

Right Front Turn Signal Lamp Control

B3949 02

B3949 05

B3949 05

--

Left Rear Turn Lamp Control

B3950 02

B3950 05

B3950 05

--

Right Rear Turn Lamp Control

B3951 02

B3951 05

B3951 05

--

Hazard Switch Ground

--

2

2

--

Left Rear Stop/Turn Lamp Ground

--

1

1

--

Repeater Lamp-Left Ground

--

1

1

--

Repeater Lamp-Right Ground

--

1

1

--

Right Rear Stop/Turn Lamp Ground

--

1

1

--

Turn Signal/Multifunction Switch Ground

--

3

3

--

Turn Signal Lamp - LF Ground

--

1

1

--

Turn Signal Lamp - RF Ground

--

1

1

--

1. Turn Signal Lamps and/or Indicators Malfunction

2. Hazard Lamps Malfunction

3. Turn Signal Switch Malfunction

Circuit/System Description

Ground is applied at all times at G201 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. Ground for the left front turn signal lamps is supplied at G101. Ground for the right front turn signal lamps is supplied at G102. Ground for the rear turn signal lamps is supplied at G302.

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 and Left Turn Signal Switch parameters while cycling the turn signal switch between the left and right positions. The parameters should chang between Active and Inactive.

If the parameters do not change between the commanded states, refer to Turn Signal Switch Malfunction.
If the parameters change between the commanded states, refer to Turn Signal Lamps Malfunction.

Circuit/System Testing

Turn Signal Switch Malfunction

  1. Ignition OFF, disconnect the X4 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal G.
  3. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  4. Ignition ON, verify the scan tool Left Turn Signal Switch parameter is Inactive.
  5. If not the specified value, test the signal circuit terminal F for a short to ground. If the circuit tests normal, replace the BCM.
  6. Verify the scan tool Right Turn Signal Switch parameter is Inactive.
  7. If not the specified value, test the signal circuit terminal H for a short to ground. If the circuit tests normal, replace the BCM.
  8. Install a 3A fused jumper wire between the signal circuit terminal F and ground. Verify the scan tool Left Turn Signal Switch parameter is Active.
  9. 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 BCM.
  10. Install a 3A fused jumper wire between the signal circuit terminal H and ground. Verify the scan tool Right Turn Signal Switch parameter is Active.
  11. 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 BCM.
  12. If all circuits test normal, test or replace the 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 ohms between the ground circuit and ground.
  3. If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Connect a test lamp between the control circuit and the ground circuit.
  5. 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.
  6. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the 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 BCM.
  7. If all circuits test normal, test or replace the appropriate turn signal lamp assembly.

Turn Signal Indicators Malfunction

Ignition ON, with a scan tool perform the Display Test for the instrument panel cluster (IPC) and observe the turn signal lamp indicators.

If the turn signal lamp indicators illuminate during the test, replace the BCM.
If the turn signal lamp indicators do not illuminate during the test or remain illuminated at all times, replace the IPC.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Repeater Lamp Replacement
    •  Tail Lamp Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM or IPC replacement, setup, and programming