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Turn Signal Lamps and/or Indicators Malfunction




Turn Signal Lamps and/or Indicators Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit/System Description

The IGN E fuse in the engine wiring harness junction block supplies Ignition positive voltage to the turn signal switch assembly. With the ignition switch in the RUN or START position, ignition positive voltage is connected through the turn signal and hazard switch assembly to the turn signal/hazard flasher module which is powered by the FLASHER fuse in the engine wiring harness junction block and is grounded at G201. When the turn signal switch is placed in either the left or right position, the circuit is complete from the turn signal/hazard flasher module to the turn signal lamps and to ground. The turn signal/hazard flasher module then sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G103 and G107. The rear turn signals are grounded at G401 and G402.

Reference Information
Schematic Reference

Exterior Lights Schematics (Exterior Lights Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Observe the left and right, front and rear turn signal lamps while the hazard switch is ON.

• If none of the lamps flash normally, refer to Hazard Lamps Malfunction.

2. Connect a test lamp between the input side LT TURN fuse and ground.
3. Ignition ON, operate the left turn switch ON and OFF. The test lamp should change from flashing ON and OFF when changing between the commanded states.

• If the test lamp is always ON or flashing, refer to the Turn Signal Switch Malfunction.
• If the test lamp is always OFF, refer to the Turn Signal Switch Malfunction.

4. Connect a test lamp between the input side RT TURN fuse and ground.
5. Operate the right turn switch ON and OFF. The test lamp should change from flashing ON and OFF when changing between the commanded states.

• If the test lamp is always ON or flashing, refer to the Turn Signal Switch Malfunction.
• If the test lamp is always OFF, refer to the Turn Signal Switch Malfunction.

6. If the flasher output circuits test normal, refer to Turn Signal Lamps Malfunction.

Circuit/System Testing

Turn Signal Switch Malfunction
1. Ignition OFF, disconnect the turn signal/multifunction switch connector X1.
2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal B and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

3. Connect the turn signal/multifunction switch connector.
4. Disconnect the turn signal/hazard flasher module connector.
5. Connect a test lamp between the left turn switch signal circuit terminal F and ground.
6. Operate the left turn switch ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the left turn switch signal circuit for a short to voltage. If the circuit tests normal, replace the turn signal/multifunction switch.
• If the test lamp is always OFF, test the left turn switch signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/multifunction switch.

7. Connect a test lamp between the right turn switch signal circuit terminal A and ground.
8. Operate the right turn switch ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the right turn switch signal circuit for a short to voltage. If the circuit tests normal, replace the turn signal/multifunction switch.
• If the test lamp is always OFF, test the right turn switch signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/multifunction switch.

9. Connect the turn signal/hazard flasher module connector.
10. Connect a test lamp between the input side LT TURN fuse and ground.
11. Operate the left turn switch ON and OFF. The test lamp should change from flashing ON and OFF when changing between the commanded states.

• If the test lamp is always ON or flashing, test the left turn lamp control circuit for a short to voltage. If the circuit tests normal, replace the turn signal/hazard flasher module.
• If the test lamp is always OFF, test the left turn lamp control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/hazard flasher module.

12. Connect a test lamp between the input side RT TURN fuse and ground.
13. Operate the right turn switch ON and OFF. The test lamp should change from flashing ON and OFF when changing between the commanded states.

• If the test lamp is always ON or flashing, test the right turn lamp control circuit for a short to voltage. If the circuit tests normal, replace the turn signal/hazard flasher module.
• If the test lamp is always OFF, test the right turn lamp control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/hazard flasher module.

Turn Signal Lamps Malfunction
1. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
2. Test for less than 5 ohms between the listed ground circuit terminal and ground.

* Front Park/Turn Signal Lamp terminal G - GMC
* Front Park/Turn Signal Lamp terminal A - Chevy, Isuzu
* Tail/Lamp Circuit Board terminal E

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

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

* Front Park/Turn Signal Lamp terminal C - GMC
* Front Park/Turn Signal Lamp terminal A - Chevy, Isuzu
* Tail Lamp Circuit Board terminal D - GMC
* Tail Lamp Circuit Board terminal B - Chevy, Isuzu

4. Ignition ON, operate the inoperative turn signal ON and OFF. The test lamp should flash 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 turn signal/hazard flasher module.
• 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 turn signal/hazard flasher module.

5. If all circuits test normal, test or replace the inoperative turn signal lamp.

Turn Signal Indicator Malfunction
1. Ignition OFF, disconnect the harness connector at the instrument panel cluster (IPC).
2. Connect a test lamp between the left turn signal indicator terminal A1 and ground.
3. Ignition ON, turn the left turn signal ON. The test lamp should blink ON and OFF.

• If the test lamp is always ON, test the signal circuit for short to voltage. If the circuit tests normal, replace the turn signal/hazard flasher module.
• If the test lamp is always OFF, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/hazard flasher module.

4. Connect a test lamp between the right turn signal indicator terminal B10 and ground.
5. Ignition ON, turn the right turn signal ON. The test should blink ON and OFF.

• If the test lamp is always ON, test the signal circuit for short to voltage. If the circuit tests normal, replace the turn signal/hazard flasher module.
• If the test lamp is always OFF, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the turn signal/hazard flasher module.

6. If all circuits test normal, replace the IPC.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Hazard and Turn Signal Flasher Replacement (Service and Repair)
* Park/Turn Signal/Side Marker Lamp Bulb Replacement (Envoy) ()Park/Turn Signal/Side Marker Lamp Bulb Replacement (TrailBlazer) (Service and Repair)
* Tail Lamp Bulb Replacement (Service and Repair)

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