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.
- Using the scan tool, erase all FCM DTCs.
- Turn the Left Turn Signals on.
- Using the scan tool, read DTCs.
Does the scan tool display: B1643-REAR LEFT TURN CONTROL CIRCUIT LOW?
Yes
- Go to step 2
No
- The condition that caused the symptom is currently not present. Inspect the related wiring for a possible intermittent condition. Look for any chafed, pierced, pinched, or partially broken wires.
- Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
- CHECK (L63) LEFT REAR TURN SIGNAL CONTROL CIRCUIT IN BODY HARNESS FOR A SHORT TO GROUND
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- Turn the ignition off.
- Disconnect the IPM C2 connector.
- Disconnect the Left Rear Turn Stop Tail Lamp connector.
- Measure the resistance of the (L63) Left Rear Turn Signal Control circuit between ground and the IPM C2 connector.
Is the resistance below 5.0 Ohms?
Yes
- Repair the (L63) Left Rear Turn Signal Control circuit for a short to ground.
- Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
No
- Go to step 3
- CHECK (L63) LEFT REAR TURN SIGNAL CONTROL CIRCUIT IN IPM FOR A SHORT TO GROUND
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- Disconnect the Front Control Module (FCM) from the IPM 49-way connector.
- Measure the resistance of the (L63) Left Rear Turn Signal Control circuit between ground and the IPM 49-way connector.
Is the resistance below 5.0 Ohms?
Yes
- Replace the Integrated Power Module (IPM) in accordance with the service information.
- Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
No
- Replace the Front Control Module (FCM) in accordance with the service information.
- Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
Use the Manual With the Right Hardware
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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.
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