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

WARNING: This page is about a different car, the 2005 Lincoln LS. 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.

F1 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.

WARNING: Never probe the electrical connector on a side air curtain module. Doing so can result in side air curtain deployment.

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: Retrieve/Record Continuous DTCs.
- 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 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 F2.
- No : This is an intermittent fault. The fault condition is not present at this time. GO to F5.
F2 INSPECT THE RCM MOUNTING, MOUNTING BRACKET AND MOUNTING SURFACE
- Key in OFF position.
- Depower the system. refer to SUPPLEMENTAL RESTRAINT SYSTEM (SRS) DEPOWERING AND REPOWERING in this article.
- Inspect the RCM retainers and RCM bracket mounting bolts and make sure they are fully seated and tightened correctly.
- Remove the RCM. REFER to RESTRAINTS CONTROL MODULE (RCM) in this article.
- Visually inspect the RCM, mounting bracket and mounting surface for damage, corrosion or dirt.
- Was a significant amount of corrosion or dirt found, or was the RCM mounting bracket 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 and mounting bracket to the mounting surface. GO to F6.
- No : GO to F3.
F3 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) in this article.
- Repower the system. Do not prove out the system at this time. refer to SUPPLEMENTAL RESTRAINT SYSTEM (SRS) DEPOWERING AND REPOWERING in this article.
- 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 F4.
- No : CHECK for causes of intermittent high resistance on circuit 31-JA10 (BK/RD) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. REPAIR any intermittent concerns found. GO to F6.
F4 CHECK GROUND CIRCUIT 31-JA10 (BK/RD) FOR HIGH RESISTANCE
- Key in OFF position.
- Depower the system. refer to SUPPLEMENTAL RESTRAINT SYSTEM (SRS) DEPOWERING AND REPOWERING in this article.
- Measure the resistance between RCM C310a pin 16, circuit 31-JA10 (BK/RD), harness side and the RCM case ground.
  
  Fig 1: Check Ground Circuit 31-JA10 (BK/RD) For High Resistance
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : INSTALL a new RCM. REFER to RESTRAINTS CONTROL MODULE (RCM) in this article. GO to F6.
- No : REPAIR circuit 31-JA10 (BK/RD). GO to F6.
F5 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 : GO to F2.
- No : CHECK for causes of intermittent high resistance on circuit 31-JA10 (BK/RD) or the chassis ground. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently. REPAIR any intermittent concerns found. GO to F6.
F6 CHECK FOR ADDITIONAL DTCs
- Refer to the continuous DTCs recorded during Step F1.
- Were any continuous DTCs retrieved during Step F1 ?
- Yes : Do not clear any DTCs until all DTCs have been resolved. GO to the RESTRAINTS CONTROL MODULE (RCM) DIAGNOSTIC TROUBLE CODE (DTC) TABLE in this article for pinpoint test direction.
- No : RECONNECT the system. REPOWER the system. refer to SUPPLEMENTAL RESTRAINT SYSTEM (SRS) DEPOWERING AND REPOWERING in this article. PROVE OUT the system. CLEAR all DTCs.