Pinpoint Test H: LFC 14/DTC B1921 - Air Bag Diagnostic Monitor Circuit Open

WARNING: This page is about a different car, the 2005 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Most faults are due to connector and/or wiring concerns. Carry out a thorough INSPECTION AND VERIFICATION before proceeding with the pinpoint test.

H1 CHECK FOR A HARD OR INTERMITTENT DTC
WARNING: Restraint system diagnostic tools are for service only. Tools must be removed prior to operating the vehicle over the road. Failure to remove restraint system diagnostic tools could result in injury and possible violation of vehicle safety standards.

WARNING: Never probe the connectors on the air bag module. Doing so can result in air bag deployment, which can result in personal injury.

WARNING: The safety belt pretensioner is a pyrotechnic device. Always wear safety glasses when repairing an air bag equipped vehicle and when handling a safety belt buckle pretensioner or safety belt retractor pretensioner. Never probe a pretensioner electrical connector. Doing so could result in pretensioner or air bag deployment and could result in personal injury.

NOTE: After diagnosing or repairing an SRS, the restraint system diagnostic tools must be removed before operating the vehicle over the road.

NOTE: The SRS must be fully operational and free of faults before releasing the vehicle to the customer.
- Enter the following diagnostic mode on the diagnostic tool: On-Demand Self Test.
- Enter the following diagnostic mode on the diagnostic tool: Retrieve/Record Continuous DTCs.
- Was DTC B1921 retrieved during the on-demand self test?
- Yes : This is a hard fault. The fault condition is still present. This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the on-demand self test. GO to H2.
- No : This is an intermittent fault. The fault condition is not present at this time. GO to H6.
H2 INSPECT THE RCM MOUNTING AND MOUNTING SURFACE
- Key in OFF position.
- Depower the system. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING .
- Inspect the RCM retainers and RCM mounting bolts and make sure they are fully seated and tightened correctly.
- Remove the RCM. Refer to RESTRAINTS CONTROL MODULE RCM .
- Visually inspect the RCM and mounting surface for damage, corrosion or dirt.
- Was a significant amount of corrosion or dirt found, or was the RCM attached to the mounting surface incorrectly or were the RCM bolts not fully seated and tightened correctly?
- Yes : CLEAN and TIGHTEN the bolts. REPAIR the mounting surface as necessary. REINSTALL the RCM to the mounting surface. GO to H7.
- No : GO to H3.
H3 INSTALL THE RCM AND CARRY OUT THE ON-DEMAND SELF TEST
- Clean the RCM mounting surfaces and bolts.
- Install the RCM. Refer to RESTRAINTS CONTROL MODULE RCM .
- Repower the system. Do not prove out the system at this time. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING .
- Enter the following diagnostic mode on the diagnostic tool: On-Demand Self Test.
- Was DTC B1921 retrieved during the on-demand self test?
- Yes : GO to H4.
- No : Fault corrected. GO to H7.
H4 CHECK GROUND CIRCUIT 1203 (BK/LB) FOR HIGH RESISTANCE
- Key in OFF position.
- Depower the system. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING .
- Disconnect: RCM C310a and C310b.
- Measure the resistance between RCM C310a pin 16, circuit 1203 (BK/LB), harness side and the RCM case ground.
  
  Fig 1: Measuring Resistance Between RCM C310a Pin 16, Circuit 1203 (BK/LB), Harness Side And RCM Case Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : GO to H5.
- No : REPAIR circuit 1203 (BK/LB). GO to H7.
H5 CONFIRM THE RCM FAULT
NOTE: Make sure all restraint system diagnostic tools, sensor electrical connectors and the RCM electrical connector are connected before carrying out the on-demand self test. If not, erroneous DTCs will be recorded.
- Key in OFF position.
- Depower the system. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING .
- Connect: RCM C310a and C310b.
- Repower the system. Do not prove out the system at this time. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING .
- Enter the following diagnostic mode on the diagnostic tool: On-Demand Self Test.
- Was DTC B1921 retrieved during the on-demand self test?
- Yes : INSTALL a new RCM. REFER to RESTRAINTS CONTROL MODULE RCM . GO to H7.
- No : Fault corrected. GO to H7.
H6 CHECK FOR AN INTERMITTENT FAULT
- Key in OFF position.
- Enter the following diagnostic mode on the diagnostic tool: On-Demand Self Test.
- Was DTC B1921 retrieved during the on-demand self test?
- Yes : This is a hard fault. The fault condition is now present. This fault cannot be cleared until it is corrected and the DTC is no longer retrieved during the on-demand self test.
  GO to H2.
- No : CHECK for causes of intermittent high resistance on circuit 1203 (BK/LB) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. ACTIVATE other systems in the same wire harness. REPAIR any intermittent concerns found. GO to H7.
H7 CHECK FOR ADDITIONAL DTCs
- Refer to the continuous DTCs recorded during Step H1.
- Were any continuous DTCs retrieved during Step H1 ?
- Yes : Do not clear any DTCs until all DTCs have been resolved. GO to the RESTRAINTS CONTROL MODULE RCM DIAGNOSTIC TROUBLE CODE (DTC) TABLE for pinpoint test direction.
- No : RECONNECT the system. If previously directed to deactivate the system, REACTIVATE the system. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEACTIVATION AND REACTIVATION . REPOWER the system. Refer to SUPPLEMENTAL RESTRAINT SYSTEM SRS DEPOWERING AND REPOWERING . PROVE OUT the system. CLEAR all DTCs.