Turn Signal Lamps and/or Indicators Malfunction
Turn Signal Lamps and/or Indicators Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.
Diagnostic Fault Information
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 body control module (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 (Exterior Lights Schematics)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Exterior Lighting Systems Description and Operation (Exterior Lighting Systems)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
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 change between Active and Inactive.
• If the parameter does not change between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.
• If the parameter does change between the specified values and the left turn signal is inoperative, refer to the Turn Signal Malfunction.
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 change between Active and Inactive.
• If the parameter does not change between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.
• If the parameter does change between the specified values and the right turn signal is inoperative, refer to the Turn Signal Malfunction.
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.
• 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.
• If the indicator is always OFF, replace the IPC.
Circuit/System Testing
Turn Signal/Multifunction Switch Malfunction
1. Ignition OFF, disconnect the X3 harness connector at the turn signal/multifunction switch.
2. Verify that a test lamp illuminates between the ground circuit terminal G and B+.
• 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 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.
• 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 3 A 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.
• 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 3 A 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.
• 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 X4 harness connector at the BCM.
2. Ignition ON, verify that a test lamp illuminates between the following B+ terminals and ground.
* 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.
3. Ignition OFF, disconnect the harness connector at the inoperative turn signal lamp.
4. Test for less than 5 ohm between the ground circuit terminal G and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
5. Connect a test lamp between the control 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.
• 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.
Outside Rearview Mirror Turn Signal Circuit Test (D25) (If Equipped)
1. Ignition OFF, disconnect the X1 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.
• 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 control circuit terminal 1 and ground.
5. 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.
• If the test lamp is always ON, test the control circuit for a short to voltage.
• If the test lamp is always OFF, test the control circuit for an open/high resistance.
6. If all circuits test normal, test or replace the outside rearview mirror lamp.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Turn Signal Multifunction Switch Replacement (Service and Repair)
* Headlamp Bulb Replacement (Service and Repair)
* Rear Turn Signal Lamp Bulb Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for BCM, IPC, and door control module replacement, setup, and programming