Test Notes

Normal Operation
The air bag diagnostic monitor measures the resistance between the ground connection at its bracket and the reference ground at pin C209-18, circuit 649 (BK/O). If the air bag diagnostic monitor measures a difference of more than 3.0 ohms between the ground at pin C209-18, circuit 649 (BK/O), and the ground at its bracket, the air bag diagnostic monitor will store in memory the Diagnostic Trouble Code (DTC) B1921 and flash Lamp Fault Code (LFC) 21 on the air bag indicator. Should the difference in resistance between pins C209-18, circuit 649 (BK/O), and air bag diagnostic monitor bracket ground be repaired or otherwise reduced to less than 3.0 ohms, the air bag diagnostic monitor will store a DTC B1921 in memory.

Possible Causes
A high resistance reading at the air bag diagnostic monitor bracket ground can be caused by:
- A poor attachment of the air bag diagnostic monitor due to loose mounting, dirt, or corrosion at the air bag diagnostic monitor bracket mounting surface(s)
- A poor reference ground at pins C208-10, circuit 650 (BK/LB), and C209-18, circuit 649 (BK/O), of the air bag diagnostic monitor.