What does it mean?
B1520 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Bonnet Latch Switch Circuit Open .
Symptoms
- Hood open warning stays displayed even with the hood firmly closed
- Alarm will not arm, or arms and then triggers on its own
- Remote start blocked by the vehicle because the hood is read as open
- Opening the hood produces no alarm response at all
- Warning appears and disappears while driving over bumps
Likely causes
- Hood ajar switch corroded internally after years of exposure to weather and washing
- Latch out of adjustment or a bent striker, so the switch plunger is never pressed fully
- Wire broken or crushed at the front of the vehicle after front end repair or bumper removal
- Connector at the switch full of water, road salt or dirt
- Switch dislodged from its bracket, or the bracket bent so the switch misses the latch
- Open in the harness between the switch and the body control module
- Insulation pad or a badly fitted hood liner holding the switch away from contact
How to fix it
- Watch the hood switch state in live data while pressing the switch by hand to see whether it changes
- Clean the switch plunger and the latch area, then check that the hood closes far enough to press it fully
- Check latch and striker adjustment, and inspect the mounting bracket for bending
- Bridge the switch connector briefly to see whether the state changes, which proves the wiring back to the module
- Inspect the front harness for crushed, chafed or previously repaired sections
- Dry out and treat the connector, or replace it if the terminals are corroded
- Replace the hood ajar switch if it does not change state reliably, then repair the harness if the fault remains