What does it mean?
B1820 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Hood Ajar Input Circuit High .
Symptoms
- Security system does not detect the hood being opened
- Alarm will not arm, or arms while showing the wrong hood state
- Hood open message never appears on the cluster even with the bonnet up
- Remote start is blocked or, on some systems, allowed when it should not be
- Under-hood lamp, where fitted, does not come on
Likely causes
- Hood ajar switch corroded, seized or misadjusted so it never closes
- Open circuit in the signal wire between the hood switch and the module
- Switch connector near the latch disconnected or full of road salt and dirt
- Signal wire shorted to battery voltage after an accessory or alarm installation
- Rodent damage to the engine bay harness
- Bent hood latch or a bonnet that no longer closes fully onto the switch plunger
- Module input failure
How to fix it
- Watch the hood status in live data while pressing the switch plunger by hand
- Clean the switch and latch area and check that the plunger moves freely
- Inspect the connector at the latch for corrosion, water and loose terminals
- Continuity test the signal wire from the switch to the module connector
- With the module unplugged, check whether battery voltage is present on the signal wire
- Adjust the hood or latch so the switch is fully depressed when closed
- Replace the hood switch or repair the harness, and consider the module only afterwards