Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Test
- INTERMITTENT CONDITION
- Turn the ignition on.
- With the scan tool, clear all DTCs.
- Turn the Left Turn Signal on.
- With the scan tool, read DTCs.
Does the scan tool display DTC: B1642-15-REAR LEFT TURN LAMP CONTROL - CIRCUIT SHORT TO BATTERY OR OPEN?
Yes
- Go To 2
No
- Test complete, the condition or conditions that originally set this DTC are not present at this time. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
- CHECK THE (L63) LEFT REAR TURN SIGNAL DRIVER CIRCUIT FOR A SHORT TO VOLTAGE IN THE HARNESS
- Turn the Left Turn Signal off.
- Turn the ignition off.
- Disconnect the Left Tail Lamp Assembly C2 harness connector.
- Disconnect the BCM E harness connector.
- Turn the ignition on.
- Measure the voltage between ground and the (L63) Left Rear Turn Signal Driver circuit.
Is there any voltage present?
Yes
- Repair the short to voltage in the (L63) Left Rear Turn Signal Driver circuit.
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
No
- Go To 3
- CHECK THE (L63) LEFT REAR TURN SIGNAL DRIVER CIRCUIT FOR AN OPEN IN THE HARNESS
- Turn the ignition off.
- Measure the resistance of the (L63) Left Rear Turn Signal Driver circuit between the Left Tail Lamp Assembly C2 harness connector and the BCM E harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 4
No
- Repair the open in the (L63) Left Rear Turn Signal Driver circuit.
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
- CHECK THE (Z914) GROUND CIRCUIT FOR AN OPEN IN THE HARNESS
- Using a 12-volt test light connected to 12-volts, check the (Z914) Ground circuit.
Does the test light illuminate brightly?
Yes
- Go To 5
No
- Repair the open in the (Z914) Ground circuit.
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
- Using a 12-volt test light connected to 12-volts, check the (Z914) Ground circuit.
- CHECK THE BCM FOR CORRECT OPERATION
- Turn the ignition off.
- Reconnect the BCM E harness connector.
- Connect a 12-volt test light between the (L63) Left Rear Turn Signal Driver circuit and the (Z914) Ground circuit at the Left Tail Lamp Assembly C2 harness connector.
- Turn the ignition on.
- Turn the Left Turn Signal on.
Does the test light blink on and off?
Yes
- Replace the Left Rear Turn Signal Bulb in accordance with the Service Information. Refer to LAMP, TAIL STOP TURN, REMOVAL .
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
No
- Replace the BCM in accordance with the Service Information. Refer to MODULE, BODY CONTROL, REMOVAL .
- Perform the BODY VERIFICATION TEST. Refer to STANDARD PROCEDURE .
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.