Possible Causes

High resistance between RCM housing ground and terminal ground could be caused by improper tightening or seating of RCM mounting bolts, damaged 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). Turn ignition switch to RUN position. Retrieve and record any continuous 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 mounting of RCM
   
   Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Inspect RCM bracket bolts and ensure bolts are fully seated and tightened properly. Remove RCM. See RESTRAINTS CONTROL MODULE (RCM)  under REMOVAL & INSTALLATION. Inspect RCM, mounting bracket and mounting surface for damage, corrosion or dirt. If bracket and mounting surface is okay and mounting bolts are tight, go to next step. If bracket and mounting surface is not okay and/or mounting bolts are not tight, repair/replace as necessary. Go to step  7 .
3. Check RCM harness connection
   
   Clean RCM mounting surface and reinstall RCM. Turn ignition switch to ON position. Perform on-demand self-test. See ON-DEMAND SELF-TEST  under DIAGNOSTICS. If DTC B1921 was retrieved during on-demand self-test, go to next step. If DTC B1921 was not retrieved, fault is corrected. Go to step  7 .
4. Check ground circuit for high resistance
   
   Turn ignition switch to OFF position. Disconnect RCM connector C310A. Measure resistance between RCM case ground and RCM connector terminal No. 16 (Black/Light/Blue wire, circuit No. 1203). See Figure . If resistance is more than 5 ohms, repair open in Light/Blue wire. See WIRING DIAGRAMS  . Go to step  7 . If resistance is less than 5 ohms, go to next step.
   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 step  7 . If DTC B1921 was not retrieved during on-demand self-test, fault is intermittent. Attempt to recreate fault by flexing wire harness and cycling ignition frequently. See WIRING DIAGRAMS  . Activate other systems in same wire harness. Repair any intermittent problems found. Go to step  7 .
6. Check for intermittent fault
   
   Turn ignition switch to OFF position. 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, attempt to recreate fault by flexing wire harness and cycling ignition switch frequently. See WIRING DIAGRAMS  . Activate other systems in same wire harness. Repair any intermittent problems found. Go to step  7 .
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 (DTC) IDENTIFICATION  table. DO NOT clear any DTCs until all DTCs have been resolved. If no continuous 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.