Failed window motor or regulator assembly, often due to worn brushes or a stripped gear.; Broken or frayed wires in the door jamb boot, caused by repeated flexing over time.; Corroded or loose electrical connectors at the motor or switch.; Faulty window switch, either the local switch or the master switch on the driver's door.; Blown fuse or tripped circuit breaker dedicated to the left rear window circuit.; Binding window tracks or glass guides that overload the motor and trigger a current fault.; Water intrusion into the door causing corrosion or short circuits in the wiring or motor.

DTC codes / B05xx · Airbags, seats, doors, lights and comfort systems / B0502

B0502Left Rear Power Window Circuit Malfunction

Q: What does code B0502 mean?

Left Rear Power Window Circuit Malfunction. B0502 indicates that the body control module (BCM) has detected an electrical fault in the left rear power window circuit, which typically includes the motor, wiring, and switch. The BCM monitors current draw and switch inputs to determine if the window is operating correctly, and it sets this code when the circuit is open, shorted, or drawing abnormal current.

B0502 indicates that the body control module (BCM) has detected an electrical fault in the left rear power window circuit, which typically includes the motor, wiring, and switch. The BCM monitors current draw and switch inputs to determine if the window is operating correctly, and it sets this code when the circuit is open, shorted, or drawing abnormal current.

SystemBody

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

The left rear window may not move at all when the switch is pressed.
The window may move slowly or intermittently, especially in cold weather.
The window may operate from the master switch but not the local switch, or vice versa.
A grinding or clicking noise may be heard from the door when the switch is activated.
Often no symptoms besides the warning light, as the window may still function normally.
The window may stop partway and refuse to move further in either direction.

Common causes, most likely first

Failed window motor or regulator assembly, often due to worn brushes or a stripped gear.
Broken or frayed wires in the door jamb boot, caused by repeated flexing over time.
Corroded or loose electrical connectors at the motor or switch.
Faulty window switch, either the local switch or the master switch on the driver's door.
Blown fuse or tripped circuit breaker dedicated to the left rear window circuit.
Binding window tracks or glass guides that overload the motor and trigger a current fault.
Water intrusion into the door causing corrosion or short circuits in the wiring or motor.

How to diagnose and fix it

Check the fuse and circuit breaker for the left rear window circuit and replace if blown.
Inspect the wiring harness in the door jamb boot for chafed or broken wires and repair as needed.
Test the window switch for continuity and proper operation, replacing it if faulty.
Measure voltage and ground at the window motor connector while operating the switch to confirm power and ground are present.
Apply direct battery power to the motor to verify it operates; if not, replace the motor or regulator assembly.
Lubricate the window tracks and guides to reduce drag and ensure smooth operation.
Clear the code and verify the repair by operating the window through several full cycles.

Before you replace the window motor

A common misdiagnosis is replacing the window motor when the actual fault is a broken wire in the door jamb boot, which is easily overlooked during a quick inspection.
The BCM may set this code if the window motor draws excessive current due to binding tracks, even though the motor itself is healthy.
In some vehicles, the left rear window circuit is controlled by a relay in the BCM; a failed relay can mimic a bad motor or switch.
After replacing a window motor or switch, the BCM may require a relearn procedure to recognize the new component and clear the code.
Water leaks into the door often cause intermittent faults that only appear after rain or a car wash, so check for moisture damage.

Can I keep driving with B0502?

The vehicle remains safe to drive because the left rear window is not a safety-critical system, but avoid operating the window repeatedly if it is stuck or making noise to prevent further damage. Have the fault repaired at your convenience to restore full window function and prevent battery drain from a stuck motor.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.