Possible Causes

Unexpected feature present could be caused by a wiring harness fault causing connection to a normally unused ECS terminal or an internal ECS module fault.

1. Check for hard or intermittent DTC
   
   Ensure ignition is off. Connect scan tool to DLC. See USING SCAN TOOL  under DIAGNOSTICS. 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 B1885 or B1886 was retrieved during on-demand self-test, fault is hard. Go to next step. If DTC B1885 or B1886 was not retrieved, fault is intermittent. Go to step  3.
2. Check ECS module connector
   
   Turn ignition off. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Access ECS module and disconnect harness connector. See ELECTRONIC CRASH SENSOR  under REMOVAL & INSTALLATION. On F-series, visually inspect ECS module harness connector terminals No. 3, 4, 5, 6, 11, 16, 18, 20, 23, 25, 26 and 27 for connections made to these normally unused terminals. See Figure. On Excursion, visually inspect ECS module harness connector terminals No. 3, 4, 5, 6, 12, 16, 18, 20, 23, 25, 26 and 27 for connections made to these normally unused terminals. If there are any connections made to normally unused terminals, repair connections as necessary. See WIRING DIAGRAMS . Go to step  3. If there are no connections made to normally unused terminals, replace ECS module. Go to step  4.
3. Check for intermittent fault
   
   Refer to continuous DTCs recorded in step  1. If DTC retrieved in step  1 was an intermittent fault, check for cause of intermittent connection to normally unused terminal(s). Attempt to recreate fault by driving vehicle, flexing wire harness and cycling ignition switch frequently. Repair any intermittent problems found. Go to next step. If DTC retrieved in step  1 was not an intermittent fault, go to next step.
4. 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. If no continuous DTCs were retrieved, reconnect air bag system. Activate air bag system. See ACTIVATING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Prove out system. Clear all DTCs. See CLEARING FAULT CODES  under DIAGNOSTICS.