Door Passenger Set Switch Stuck Failure
The passenger door's window control switch is physically stuck in one position, preventing normal operation—like a light switch frozen in place. The ECU detects this because the switch isn't sending the expected electrical signals when commanded to move.
The ECU monitors voltage signals from the passenger door switch circuit to detect normal open/close transitions. When a switch command is sent, the ECU expects the signal to change states within a normal timeframe. A stuck switch produces no signal change or an abnormal resistance value, indicating a mechanical failure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Switch Signal Transition | Voltage changes 0-12V within 500ms of button press | No voltage transition or stuck at single voltage level |
| Switch Resistance | 0-100 ohms (closed) or 10k+ ohms (open) | Resistance remains constant regardless of actuation attempt |
Code B2120 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, B2120 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.