Possible Causes

WARNING: This page is about a different car, the 2004 Mercury Monterey and 2004 Ford Freestar. However, it is still accessible from the selected car via links, so may be relevant.

A seat belt tension sensor fault could be caused by damaged wiring, terminals, or connectors, open circuit, short to battery, short to ground, faulty seat belt tension sensor or faulty RCM.

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, flag and record any continuous Diagnostic Trouble Codes (DTCs). See RETRIEVING FAULT CODES under DIAGNOSTICS. Retrieve and record any flagged faults. Perform on-demand self-test. See ON-DEMAND SELF-TEST under DIAGNOSTICS. Flag DTC B2909. See BIT-MAPPED DIAGNOSTIC TROUBLE CODES under DIAGNOSTICS. Retrieve and record any flagged faults. If DTC B2909 was retrieved during on-demand self-test, fault is hard. If flagged fault of "?" was recorded, multiple faults exist and entire test must be carried out.
- For seat belt tension sensor with circuit fault (FTPS-F), go to next step.
  For seat belt tension sensor with an short to ground fault (FTPS-SG), go to step 4 .
If DTC B2909 was not retrieved, fault is intermittent. Go to step 9 .

Check seat belt tension sensor for short to battery

Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM under DISABLING & ACTIVATING AIR BAG SYSTEM. Access seat belt tension sensor and disconnect harness connector C3238. See RIGHT FRONT SEAT BELT/SEAT BELT TENSION SENSOR ASSEMBLY under REMOVAL & INSTALLATION. Access OCS module and disconnect harness connector C3043. See OCCUPANT CLASSIFICATION SENSOR (OCS) under REMOVAL & INSTALLATION. Turn ignition switch to ON position. Measure voltage between ground and harness side of OCS module connector C3042, terminals "B" (Tan/Red wire, circuit No. 2088), "C" (Dark Blue/Orange wire, circuit No. 2090) and "A" (Orange/Black wire, circuit No. 2089). See Figure . If voltage is less than 0.2 volt in all circuits, go to next step. If voltage is more than 0.2 volt in any circuit, repair short to battery in appropriate wire. See WIRING DIAGRAMS . Go to step 10 .

Check seat belt tension sensor for open

Turn ignition switch to OFF position. Measure resistance between harness side of OCS module connector C3043, terminal "B" and harness side of seat belt tension sensor connector C3238, terminal No. 1 (Tan/Red wire). See Figure & Fig 1 . Measure resistance between harness side of OCS module connector C3043, terminal "C" and harness side of seat belt tension sensor connector C3238, terminal No. 2 (Dark Blue/Orange wire). Measure resistance between harness side of OCS module connector C3042, terminal "A" and harness side of seat belt tension sensor connector C3238, terminal No. 3 (Orange/Black wire). If resistance is less than 0.5 ohm, go to step 5 . If resistance is more than 0.5 ohm, repair open in appropriate wire. Go to step 10 .

Check seat belt tension sensor for short to ground

Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM under DISABLING & ACTIVATING AIR BAG SYSTEM. Access seat belt tension sensor and disconnect harness connector C3238. See RIGHT FRONT SEAT BELT/SEAT BELT TENSION SENSOR ASSEMBLY under REMOVAL & INSTALLATION. Access OCS module and disconnect harness connector C3043. See OCCUPANT CLASSIFICATION SENSOR (OCS) under REMOVAL & INSTALLATION. Turn ignition switch to ON position. Measure resistance between ground and harness side of OCS module connector C3043, terminals "B" (Tan/Red wire, circuit No. 2088), "C" (Dark Blue/Orange wire, circuit No. 2090) and "A" (Orange/Black wire, circuit No. 2089). See Figure . If resistance is more than 10 k/ohms in all circuits, go to next step. If resistance is less than 10 k/ohms in any circuit, repair short to ground in appropriate wire. See WIRING DIAGRAMS . Go to step 10 .

Check circuits for short

Measure resistance between harness side of OCS module connector C3043, terminal "B" (Tan/Red wire) and "A" (Orange/Black wire). Measure resistance between harness side of OCS module connector C3043, terminal "B" (Tan/Red wire) and "C" (Dark Blue/Orange wire). Measure resistance between harness side of OCS module connector C3043, terminal "A" (Orange/Black wire) and "C" (Dark Blue/Orange wire). If resistance is more than 10 k/ohms between all circuits, go to next step. If resistance is less 10 k/ohms between any circuit, repair short between appropriate wires. Go to step 10 .

Check OCS module output

Reconnect OCS module connector C3043. Turn ignition switch to ON position. Measure voltage between harness side of seat belt tension sensor connector C3238, terminals No. 1 (Tan/Red wire) and No. 2 (Dark Blue/Orange wire). See Fig 1 . If voltage is about 5 volts, go to next step. If resistance is not about 5 volts, replace OCS system.

Check seat belt tension sensor voltage output

Turn ignition switch to OFF position. Connect fused jumper between harness and component side of seat belt tension sensor connector C3238, terminal No. 1. Connect fused jumper between harness and component side of seat belt tension sensor connector C3238, terminal No. 2. Turn ignition switch to ON position. Measure voltage between ground and component side of seat belt tension sensor connector C3238, terminal No. 3 (Orange/Black wire) while varying tension on seat belt tension sensor. If voltage varies between 0.95 volt with no tension on seat belt tension sensor, and 3.8 volts with full tension on seat belt tension sensor, go to next step. If voltage does not vary between 0.95 volt with no tension on seat belt tension sensor, and 3.8 volts with full tension on seat belt tension sensor, replace seat belt tension sensor. Go to step 10 .
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.

Confirm seat belt tension sensor fault

Turn ignition switch to OFF position. Reconnect OCS module connector C3043. Reconnect seat belt tension sensor connector C3238. Turn ignition switch to ON position. Perform on-demand self-test. Flag DTC B2909. Retrieve and record flagged DTCs. If DTC B2909 was retrieved during on-demand self-test, replace OCS system. Go to step 10 . If DTC B2909 was not retrieved during on-demand self-test, 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 step 10 .

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. Flag DTC 2909.
If DTC B2909 was retrieved during on-demand self-test, retrieve and record any flagged faults. Use flagged faults to find appropriate step. If flagged fault "?" was recorded, multiple faults exist and entire test must be carried out.
- For seat belt tension sensor with circuit fault (FTPS-F), go to step 2 .
  For seat belt tension sensor with an short to ground fault (FTPS-SG), go to step 4 .
If DTC B2909 was not retrieved during on-demand self-test, fault is intermittent. 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.

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. Activate air bag system. See ACTIVATING SYSTEM under DISABLING & ACTIVATING AIR BAG SYSTEM. Clear all DTCs. See CLEARING FAULT CODES under DIAGNOSTICS.

Fig 1: Identifying Seat Belt Tension Sensor Connector C3238 Terminals

Courtesy of FORD MOTOR CO.