Test J: LFC 21/DTC B1921 - RCM Bracket Ground Resistance High

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J2:

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Normal Operation

WARNING: THE TIGHTENING TORQUE OF THE RESTRAINTS CONTROL MODULE (RCM) RETAINING BOLTS IS CRITICAL FOR CORRECT AIR BAG SUPPLEMENTAL RESTRAINT SYSTEM (SRS) OPERATION.

NOTE: A resistance difference as low as 10 ohms may set the LFC.

The Restraints Control Module (RCM) monitors the resistance between the ground connections at the mounting bracket and the reference ground at C310a pin 10, circuit 649 (BK/OG). If the RCM detects a difference in resistance, it will store Diagnostic Trouble Code (DTC) B1921 in memory and flash Lamp Fault Code (LFC) 21 (or higher priority code if one exists) on the air bag indicator.

Possible Causes
A resistance difference between the RCM bracket ground and harness ground can be caused by:
^ an RCM internal concern.
^ incorrect tightening torque of the RCM retaining bolts.
^ high resistance on RCM logic ground circuit 649 (BK/OG).
^ a chassis grounding concern.