Door Ajar LR Circuit Failure
The left rear door sensor is not communicating properly with the car's computer, like a broken intercom between the door and the brain of the vehicle. This prevents the system from knowing if the door is open or closed.
The ECU monitors the door ajar switch circuit voltage to determine door position. When the door opens, the switch closes and pulls the signal low; when closed, the circuit should return high. A failure occurs when the ECU detects an open circuit or abnormal voltage that doesn't match expected state transitions.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Door Ajar Signal Voltage | 0V (door open) to 5V (door closed) | No signal, stuck voltage, or erratic transitions |
| Circuit Continuity | Complete path <10 ohms | Open circuit >100k ohms or shorted to ground |
Code B1571 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1571 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.