Test Notes

Normal Operation
The air bag Electronic Crash Sensor (ECS) module monitors the resistance between the ground connections at its housing and the reference ground at Pins 21 and 22. If the ECS detects a resistance greater than 100 ohms, it will store a Diagnostic Trouble Code (DTC) B1921 in memory and flash a Lamp Fault Code (LFC) 21 (or higher priority code if one exists) on the air bag indicator.

Possible Causes
High resistance between the ECS module housing ground and pin ground could be caused by:
^ improper tightening torque of the ECS module retaining bolts.
^ high resistance on both ECS logic grounds.