Possible Causes

High resistance between RCM housing ground and terminal ground could be caused by improper seating or tightening of RCM mounting bolts, or damaged wiring, connectors or terminals.

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 ON 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. Access RCM. See RESTRAINTS CONTROL MODULE (RCM)  under REMOVAL & INSTALLATION. Inspect RCM, mounting bracket and mounting surface for damage or corrosion. Inspect RCM bracket bolts are fully seated and tightened properly. 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
   
   Ensure RCM harness connector is fully connected. If RCM harness connector is fully connected, go to next step. If RCM harness connector is not fully connected, reattach connector. Go to step  7 .
4. Check vehicle chassis ground
   
   Measure resistance between a known good ground and RCM mounting surface. If resistance more than 100 ohms, repair grounding system and go to step  7 . If resistance is less than 100 ohms, go to next step.
5. Check ground circuit for open
   
   Disconnect RCM harness connector. Measure resistance between chassis ground and RCM harness connector C2041, terminal No. 21 (Black/White wire, circuit No. 570). See Figure . If resistance is more than 10 ohms, repair open in Black/White wire. See WIRING DIAGRAMS  . Go to step  7 . If resistance is less than 10 ohms, replace RCM. 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. Turn ignition switch to ON position. Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, check for intermittent fault in Black/White wire. Repair any intermittent problems found. If intermittent problems are found and repaired, go to next step. If intermittent problems are not found, go to step  2 . If DTC B1921 was not retrieved, check for cause of intermittent fault. Attempt to recreate fault by flexing wire harness and cycling ignition switch frequently. Activate systems in same wire harness. See WIRING DIAGRAMS  . 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. DO NOT clear any DTCs until all DTCs have been resolved. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION  table. If no continuous DTCs were retrieved, reconnect air bag system. Reactivate air bag system. See ACTIVATING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Perform system operation check. See SYSTEM OPERATION CHECK  . Clear all DTCs. See CLEARING FAULT CODES  under DIAGNOSTICS.