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 |
|---|---|---|---|---|
Left Turn Signal Switch Signal | 1, 3 | 1, 3 | 1, 3 | -- |
Right Turn Signal Switch Signal | 2, 4 | 2, 4 | 2, 4 | -- |
Left Front Turn Signal Lamp Supply Voltage | B3948 | B3948 | B3948 | -- |
LF Park/Turn Signal Lamp Ground | 1 | 1 | 1 | -- |
Right Front Turn Signal Lamp Supply Voltage | B3949 | B3949 | B3949 | -- |
RF Park/Turn Signal Lamp Ground | 2 | 2 | 2 | -- |
Left Rear Stop/Turn Signal Lamp Supply Voltage | B3950 | B3950 | B3950 | -- |
Left Tail/Stop and Turn Signal Lamp Ground | 3 | 3 | 3 | -- |
Right Rear Stop/Turn Signal Lamp Supply Voltage | B3951 | B3951 | B3951 | -- |
Left Tail/Stop and Turn Signal Lamp Ground | 4 | 4 | 4 | -- |
Turn Signal/Multifunction Switch Ground | -- | 1, 2, 3, 4 | 1, 2, 3, 4 | -- |
1. Left Front Park/Turn Signal Inoperative 2. Right Front Park/Turn Signal Inoperative 3. Left Rear Stop/Turn Signal Inoperative 4. Right Rear Stop/Turn Signal Inoperative | ||||
Circuit/System Description
The Body Control Module (BCM) controls the turn signals based on an input from the turn signal switch, part of the multifunction turn signal lever. The BCM receives an input from one of two signal circuits to determine which turn signal function is requested. When the turn signal lever is placed in the LEFT position, the left turn signal switch signal circuit is grounded indicating that left turn signal operation is requested. When the turn signal lever is placed in the RIGHT position, the right turn signal switch signal circuit is grounded indicating that right turn signal operation is requested.
When a turn signal input is received from the turn signal switch, the BCM will activate the appropriate turn signals. The BCM pulses voltage to the applicable turn signals via the turn signal lamp supply voltage circuits, illuminating the required turn signal lamps.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Ignition ON, observe the scan tool BCM Left Turn Signal parameter while turning the left turn signal ON and OFF with the turn signal multifunction lever. The parameter should change between On and Off.
- Ignition ON, observe the scan tool BCM Right Turn Signal parameter while turning the right turn signal ON and OFF with the turn signal multifunction lever. The parameter should change between On and Off.
- Command the appropriate turn signal lamp ON and OFF with a scan tool. The appropriate turn signal lamp should turn ON and OFF when changing between the commanded states.
| ⇒ | If the parameter does not change between the specified values, refer to Turn Signal Switch Circuit Malfunction. |
| ⇒ | If the parameter does not change between the specified values, refer to Turn Signal Switch Circuit Malfunction. |
| ⇒ | If the appropriate turn signal lamp does not cycle between the commanded states, refer to Turn Signal Circuit Malfunction. |
Circuit/System Testing
Turn Signal Switch Circuit Malfunction
- Ignition OFF, disconnect the X2 harness connector at the turn signal multifunction lever.
- Test for less than 5 ohms between the ground circuit terminal G and ground.
- Ignition ON, verify the scan tool BCM Left Turn Signal parameter is Off.
- Verify the scan tool BCM Right Turn Signal parameter is Off.
- Install a 3A fused jumper wire between the signal circuit terminal F and the ground circuit terminal G. Verify the scan tool BCM Left Turn Signal parameter is On.
- Install a 3A fused jumper wire between the signal circuit terminal H and the ground circuit terminal G. Verify the scan tool BCM Right Turn Signal parameter is On.
- If all circuits test normal, test or replace the turn signal multifunction lever.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If not the specified value, test the signal circuit terminal F for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If not the specified value, test the signal circuit terminal H for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | 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. |
| ⇒ | 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. |
Turn Signal Circuit Malfunction
- Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp bulb.
- Test for less than 10 ohms between the ground circuit terminal C (Front) or G (Rear) and ground.
- Install a test lamp between the signal circuit terminal A and ground.
- Ignition ON, command the appropriate turn signal lamp ON and OFF with a scan tool. The appropriate turn signal lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the appropriate turn signal lamp bulb.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
| ⇒ | If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
