B1520: Hood Switch Circuit Open

B1520 is a body electronics code indicating an open circuit in the hood switch circuit. The hood switch, sometimes called a bonnet switch in Australian terminology, is a small sensor that tells the body control module whether the bonnet is open or closed. It feeds data to the vehicle's security and alarm system, and in some vehicles also to underbonnet lighting circuits. When the BCM sees no signal from this switch when it expects one, or detects infinite resistance indicating an open circuit, B1520 is logged.

The most likely causes are a failed or stuck switch that no longer makes contact, a broken or corroded connector at the switch, or a break in the wiring between the switch and the BCM. The switch itself is typically a simple plunger-type unit mounted on the bonnet latch or body panel, and it is exposed to moisture, road grime, and temperature cycling which can cause it to fail or corrode over time. Locating the switch, testing for continuity, and inspecting the connector is usually enough to confirm whether the switch or the wiring is at fault.

This is a medium-severity code. Your vehicle will drive normally, but the security system may not correctly detect bonnet-open events, which can affect alarm operation or trigger false alerts. It is not urgent in the mechanical sense, but if you rely on your vehicle's security system it is worth addressing within a reasonable timeframe. The repair is typically straightforward and inexpensive.