Turn Signal Lamps and/or Indicators Malfunction
Turn Signal Lamps and/or Indicators Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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/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 also 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.
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. 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 and off when changing between the commanded states.
^ If the test lamp is always on or flashing, refer to the turn signal switch circuit test.
^ If the test lamp is always off, refer to the turn signal switch circuit test.
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 and off when changing between the commanded states.
^ If the test lamp is always on or flashing, refer to the turn signal switch circuit test.
^ If the test lamp is always off, refer to the turn signal switch circuit test.
6. If the flasher output circuits test normal, refer to turn signal lamps circuit test.
Circuit/System Testing
Turn Signal Switch Circuit Test
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. Ignition ON, 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. Ignition ON, 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. Ignition ON, operate the left turn switch on and off. The test lamp should change from flashing 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 an open/high resistance or short to ground. 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 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 an open/high resistance or short to ground. If the circuit tests normal replace the turn signal/hazard flasher module.
Turn Signal Lamps Circuit Test
1. Ignition OFF, disconnect the harness connector at the affected turn signal lamp.
2. Test for less than 1 ohm between the listed ground circuit terminal and ground.
* Front Chevy terminal A
* Front GMC, Isuzu terminal G
* Rear 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 circuit terminal.
* Front Chevy terminal C to terminal A
* Front GMC, Isuzu terminal A to terminal G
* Rear Chevy, Isuzu terminal B to terminal E
* Rear GMC terminal D to terminal E
4. Ignition ON, operate the affected turn signal ON and OFF. The test lamp should flash and turn 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 affected turn signal lamp.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Hazard and Turn Signal Flasher Replacement
* Park/Turn Signal/Side Marker Lamp Bulb Replacement (Envoy) Park/Turn Signal/Side Marker Lamp Bulb Replacement (TrailBlazer)
* Tail Lamp Bulb Replacement