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 a difference of more than 3.0 ohms between the ground at Pin C209-18 and the air bag diagnostic monitor bracket ground, the air bag diagnostic monitor will store a Diagnostic Trouble Code (DTC) B1921 in memory and flash a Lamp Fault Code (LFC) 21 on the air bag indicator to indicate a possible open ground circuit. Should the difference of more than 3.0 ohms of resistance between Pin C209-18, Circuit 649(BK/O) and the air bag diagnostic monitor bracket ground be intermittent or repaired, 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:
^ poor attachment of the air bag diagnostic monitor due to loose mounting, dirt, or corrosion at the air bag diagnostic monitor bracket mounting surface.
^ 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.