Possible Causes

Resistance difference between RCM bracket ground and harness ground could be caused by improper tightening of RCM mounting bolts, faulty wiring, terminals or connectors or faulty RCM.

1. Check for hard or intermittent DTC
   
   Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). See USING SCAN TOOL  under DIAGNOSTICS. Turn ignition switch to ON position. Retrieve and record any continuous Diagnostic Trouble Codes (DTCs). See RETRIEVING FAULT CODES  under DIAGNOSTICS. Perform on-demand self-test. See ON-DEMAND SELF-TEST  under DIAGNOSTICS. If DTC B1921 was retrieved during on-demand self-test, fault is hard. Go to next step. If DTC B1921 was not retrieved, fault is intermittent. Go to step  6 .
2. Check RCM mounting & bracket
   
   Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Access RCM. See RESTRAINTS CONTROL MODULE (RCM)  under REMOVAL & INSTALLATION. Inspect RCM mounting and ensure retaining bolts are fully seated and tightened properly. Remove RCM and visually inspect mounting bracket and mounting surface for damage, corrosion or dirt. If problems are found, repair or replace as necessary. Install RCM and mounting bracket to mounting surface. Tighten RCM mounting bolts to specification. See TORQUE SPECIFICATIONS  . Go to step  7 . If no problems were found, go to next step.
3. Install RCM and perform on-demand self-test
   
   Clean mounting surface and bolts. Install RCM and mounting bracket to mounting surface. Tighten RCM mounting bolts to specification. Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, go to next step. If DTC B1921 was not retrieved during on-demand self-test, fault is corrected. Go to step  7 .
4. Check ground circuit for high resistance
   
   Turn ignition switch to OFF position. Measure resistance between harness side of RCM connector C310A, terminal No. 16 (Black/Light Blue wire, circuit No. 1203) and RCM case ground. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair high resistance in Black/Light Blue wire. See WIRING DIAGRAMS  . Go to step  7 .
   NOTE: Ensure all air bag system simulators, sensor electrical connectors and RCM electrical connectors are connected prior to carrying out on-demand self-test or erroneous faults may be set.
5. Confirm RCM fault
   
   Turn ignition switch to OFF position. Reconnect RCM connector C310A. Turn ignition switch to ON position. Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, replace RCM. Go to next step. If DTC B1921 was not retrieved during on-demand self-test, check for cause of intermittent open or short to ground in Light Blue/Pink wire. Attempt to recreate fault by flexing wire harness and cycling ignition switch frequently. Activate other systems in same wire harness. Repair any intermittent problems found. Go to next step.
6. Check for intermittent fault
   
   Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, go to step  2 . If DTC B1921 was not retrieved during on-demand self-test, check for cause of intermittent high resistance in Black/Light Blue wire (circuit No. 1203) or chassis ground. See WIRING DIAGRAMS  . Attempt to recreate fault by flexing wire harness and cycling ignition switch frequently. Activate other systems in same wire harness. Repair any intermittent problems found. Go to next step.
7. Check for additional DTCs
   
   Refer to continuous DTCs recorded in step  1 . If any continuous DTCs were retrieved, go to diagnostic trouble code identification table for direction to appropriate test. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table. DO NOT clear any DTCs until all DTCs have been resolved. If no DTCs were retrieved, reconnect air bag system. Reactivate air bag system. See ACTIVATING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Clear all DTCs. See CLEARING FAULT CODES  under DIAGNOSTICS.