Decklid Ajar Rear Door Circuit Failure
Your car's rear door or trunk lid sensor is sending a bad electrical signal, like a light switch that's broken and won't properly report if the door is open or closed. The car can't trust whether the door is actually ajar or sealed.
The ECU monitors the rear door/decklid latch switch circuit for proper voltage transitions when the door opens and closes. It expects a clean signal transition between open (high voltage) and closed (low voltage) states. A circuit failure means the signal is stuck, intermittent, or shorted.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Decklid Switch Signal | Clean transition 0V-5V or 0.5V-4.5V | Stuck voltage, no transition, or short to ground |
| Circuit Resistance | < 10 ohms closed, > 100k ohms open | Out-of-range resistance or open circuit |
Code B1331 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, B1331 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.