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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2007 🢒 Lucerne 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Turn Signal Lamps and/or Indicators Malfunction

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

B+, BCM C4 Terminal 1

2

2

--

--

B+, BCM C4 Terminal 2

B2615 00

B2615 00

--

--

B+, BCM C4 Terminal 3

7

7

--

--

Left Front Turn Signal Lamp Supply Voltage

2

4, 8

4

--

Right Front Turn Signal Lamp Supply Voltage

B2615 00

5, 9

5

--

Left Rear Stop/Turn Lamp Supply Voltage

2

6

6

--

Right Rear Stop/Turn Lamp Supply Voltage

7

7

7

--

Left Turn Signal Switch Signal

1, 2

2

2

--

Right Turn Signal Switch Signal

1

3

3

--

Left Outside Rearview Mirror Turn Signal Lamp Low Reference

--

8

--

--

Right Outside Rearview Mirror Turn Signal Lamp Low Reference

--

9

--

--

LF Park/Turn Signal Lamp Ground

--

4

--

--

RF Park/Turn Signal Lamp Ground

--

5

--

--

Left Tail Stop/Turn Lamp Ground

--

6

--

--

Right Tail Stop/Turn Lamp Ground

--

7

--

--

Turn Signal/Multifunction Switch Ground

--

1

--

--

  1. All turn signals inoperative
  2. Left turn signal malfunction
  3. Right turn signal 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 outside rearview mirror turn signal malfunction
  9. Right outside rearview mirror turn signal malfunction

Circuit/System Description

Ground is applied at all times to the turn signal/multifunction switch from G300. The turn signal lamps may only be activated with the ignition switch in the ON position. The BCM controls the vehicle turn signals based on inputs from the turn signal/multifunction switch. With the turn signal/multifunction switch in either the left or right turn position, a ground is applied through the turn signal switch signal circuit to the BCM indicating a turn signal request. When the specific request is seen, the BCM then applies a pulsating voltage through the front and rear turn signal supply voltage circuits illuminating the turn signal lamps.

When a turn signal request is seen by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the respective turn signal indicator be pulsed.

Reference Information

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification
  1. Ignition ON, observe the scan tool Left Turn Signal Switch parameter while using the turn signal/multifunction switch to turn the left turn signal on and off. The parameter should cycle between Active and Inactive.
    2. ⇒If the parameter does not cycle between the specified values, refer to Turn Signal/Multifunction Switch Circuit Test.
    ⇒If the parameter does cycle between the specified values and the left turn signal is inoperative, refer to the Turn Signal Circuit Test.
  2. Observe the scan tool Right Turn Signal Switch parameter while using the turn signal/multifunction switch to turn the right turn signal on and off. The parameter should cycle between Active and Inactive.
    3. ⇒If the parameter does not cycle between the specified values, refer to Turn Signal/Multifunction Switch Circuit Test.
    ⇒If the parameter does cycle between the specified values and the right turn signal is inoperative, refer to the Turn Signal Circuit Test.
  3. Ignition ON, place the turn signal/multifunction switch in the left turn position. The left turn signal indicator on the IPC should cycle ON and OFF.
    4. ⇒If the indicator is always OFF, replace the IPC.
  4. Ignition ON, place the turn signal/multifunction switch in the right turn position. The right turn signal indicator on the IPC should cycle ON and OFF.
    5. ⇒If the indicator is always OFF, replace the IPC.

Circuit/System Testing

Turn Signal/Multifunction Switch Circuit Test.

  1. Ignition OFF, disconnect the (C3) harness connector at the turn signal/multifunction switch.
  2. Verify that a test lamp illuminates between the ground circuit terminal G and B+.
    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.
    4. ⇒If not the specified value, test the signal circuit terminal F for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool Right Turn Signal Switch parameter is Inactive.
    5. ⇒If not the specified value, test the signal circuit terminal H for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3A fused jumper wire between the signal circuit terminal F and the ground circuit terminal G. Verify the scan tool Left Turn Signal Switch parameter is Active.
    6. ⇒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.
  6. Install a 3A fused jumper wire between the signal circuit terminal H and the ground circuit terminal G. Verify the scan tool Right Turn Signal Switch parameter is Active.
    7. ⇒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.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Turn Signal Circuit Test.

  1. Ignition OFF, disconnect the (C4) harness connector at the BCM.
  2. Ignition ON, verify a test lamp illuminates between the following B+ terminals and ground.
    3. • B+ terminal 1
    • B+ terminal 2
    • B+ terminal 3
    ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit fuse is open, test the B+ circuit and the respective turn signal circuits for a short to ground.
  3. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
  4. Test for less than 5.0 ohms of resistance between the ground circuit terminal G and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Connect a test lamp between the supply voltage circuit terminal A and the ground circuit terminal G.
  6. Ignition ON, command the inoperative turn signal 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 supply voltage circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    ⇒If the test lamp is always OFF, test the supply voltage 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.

Outside Rearview Mirror Turn Signal Circuit Test

  1. Ignition OFF, disconnect the (C1) harness connector at the inoperative outside rearview mirror.
  2. Connect a test lamp between the low reference circuit terminal 2 and B+.
  3. Ignition ON, command the appropriate LF or RF Turn Signal ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    4. ⇒If the test lamp is always ON, test the low reference circuit for a short to ground. If the circuit tests normal, replace the door module.
    ⇒If the test lamp is always OFF, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the door module.
  4. Connect a test lamp between the supply voltage circuit terminal 1 and ground.
  5. Ignition ON, command the appropriate LF or RF Turn Signal 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 supply voltage circuit for a short to voltage.
    ⇒If the test lamp is always OFF, test the supply voltage circuit for an open/high resistance.
  6. If all circuits test normal, test or replace the outside rearview mirror lamp bulb.

Component Test

Turn Signal/Multifunction Switch

  1. Ignition OFF, disconnect the (C3) harness connector at the turn signal/multifunction switch.
  2. Test for infinite resistance between the following terminals and the ground circuit terminal E with the switch in the neutral position.
    3. • Signal terminal F
    • Signal terminal H
    ⇒If not the specified value, replace the turn signal/multifunction switch.
  3. Test for less than 2.0 ohms of resistance between the signal circuit terminal D and the ground circuit terminal E with the switch in the left turn position.
    4. ⇒If greater than the specified range, replace the turn signal/multifunction switch.
  4. Test for less than 2.0 ohms of resistance between the signal circuit terminal F and the ground circuit terminal E with the switch in the left turn position.
    5. ⇒If greater than the specified range, replace the turn signal/multifunction switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Turn Signal Multifunction Switch Replacement
    •  Headlamp Bulb Replacement
    •  Rear Turn Signal Lamp Bulb Replacement
    •  Control Module References for BCM, IPC, and door control module replacement, setup, and programming