Hood Switch Circuit Open
The hood switch circuit isn't sending a signal to the ECU, like a light switch that's broken and can't tell if the hood is open or closed. This is typically a wiring or switch failure rather than an engine performance issue.
The ECU monitors the hood switch circuit for voltage changes when the hood opens and closes. It expects a signal transition between closed (high voltage) and open (low voltage) states. When no signal is detected or the circuit remains in a single state, the ECU logs a fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Hood Switch Signal | Voltage transitions 0V to 12V when toggled | No voltage change or stuck at single state for 2+ seconds |
| Circuit Resistance | < 10 ohms closed, > 100k ohms open | Out of range or open circuit detected |
Code B1520 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, B1520 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.