B1921: Airbag Diagnostic Monitor Ground Open
The B1921 code indicates that the airbag system control module (Restraints System Activation and Status Module or Diagnostic Monitor) has detected an open circuit in the ground circuit of the airbag diagnostic monitor. This ground reference is essential for the module to perform self-diagnostics and communicate properly with sensors and actuators in the passive safety system. Without a stable ground, the diagnostic monitor cannot verify the integrity of airbag circuits or ensure deployment in a collision. This code is specific to Ford Motor Company and its associated brands, where the airbag system uses a separate diagnostic monitor with its own dedicated ground circuit. An open in this circuit can prevent airbag deployment during an accident, posing a significant safety risk.
1. Commonly Affected Makes
2. Most Common Causes
- Broken, corroded, or disconnected ground wire for the airbag diagnostic monitor
- Loose or corroded ground terminal at the airbag control module connector
- Blown or damaged ground fuse in the airbag circuit
- Internal ground fault within the airbag control module (Diagnostic Monitor)
- Damaged wiring harness in the airbag system due to chafing or corrosion
- Airbag module connector not fully seated after previous repairs
3. Symptoms You Will Notice
- Airbag warning light illuminated on the dashboard
- Diagnostic trouble code B1921 stored in the airbag system
4. Step-by-Step Diagnosis
Scan the airbag system for codes and verify B1921 is present.
Visually inspect the ground wire and connections for the airbag diagnostic monitor; look for breaks, corrosion, or loose terminals.
Check the ground fuse in the airbag circuit and replace if open.
Test continuity of the ground circuit from the module connector to chassis ground.
If wiring and fuse are good, suspect a faulty airbag control module and perform module self-test or replacement.
5. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive. The airbags may not deploy in a crash, increasing the risk of injury. Have the vehicle repaired immediately.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the issue is a simple ground wire repair or requires replacement of the airbag control module.