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. |
DTC Descriptor
DTC B3948: Left Front Turn SignalDTC B3949: Right Front Turn Signal
DTC B3950: Left Rear Turn Signal
DTC B3951: Right Rear Turn Signal
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
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 | -- |
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.
Conditions for Running the DTC
A turn signal input is received from the turn signal switch
Conditions for Setting the DTC
B3948
A short to voltage, short to ground, or an open/high resistance is seen on the left front turn signal lamp supply voltage circuit
B3949
A short to voltage, short to ground, or an open/high resistance is seen on the right front turn signal lamp supply voltage circuit
B3950
A short to voltage, short to ground, or an open/high resistance is seen on the left rear stop/turn signal lamp supply voltage circuit
B3951
A short to voltage, short to ground, or an open/high resistance is seen on the right rear stop/turn signal lamp supply voltage circuit
Action Taken When the DTC Sets
The applicable turn signal is disabled
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists |
| • | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred |
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, 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.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate turn signal lamp bulb.
- Test for less than 10 ohms of resistance between the ground circuit terminal G (Rear - All; Front - L26/L32 only) or 3 (Front - LS4 only) and ground.
- Install a test lamp between the signal circuit terminal A (Rear - All; Front - L26/L32 only) or 1 (Front - LS4 only) 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 |
