B1921: Air Bag Diagnostic Monitor Ground Circuit Open
CriticalBodyRestraint System
What does B1921 mean?
B1921 is a diagnostic trouble code indicating "Air Bag Diagnostic Monitor Ground Circuit Open". This means there is an electrical break in the restraint system wiring — a connector may be unplugged, a wire broken, or a component has failed internally. The ECU detected no signal where it expected one.
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed restraint system sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This is a critical issue. Stop driving as soon as it is safe to do so and have the vehicle inspected immediately. Continuing to drive could cause further damage or pose a safety risk.
Get a diagnosis for YOUR car
Code B1921 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.