Ford Mustang Service Manual: Pinpoint Test B: LFC 21/DTC B1921 - RCM Bracket Ground Resistance High

Ford Mustang Service Manual / Body / Supplemental Restraint System / Pinpoint Tests - Air Bag Supplemental Restraint System (SRS) / Pinpoint Test B: LFC 21/DTC B1921 - RCM Bracket Ground Resistance High

Pinpoint Test A: The Air Bag Warning Indicator Is Illuminated Continuously - RCM Disconnected, Inoperative or Lost/Low Ignition Feed

Normal Operation

NOTE: During normal operation the air bag indicator will be lit continuously for 6 seconds after the ignition switch is placed in the RUN position and after five cycles of a lamp fault code (LFC) if a fault exists. Be sure to cycle the ignition switch and look for a 6 second indicator prove-out without LFCs.

The restraints control module (RCM) will communicate diagnostic trouble codes (DTCs) to the scan tool through the data link connector (DLC). If the scan tool displays NO COMMUNICATION when retrieving continuous DTCs, Go To Pinpoint Test P to troubleshoot the system.

Possible Causes

An air bag indicator that is illuminated continuously can be caused by one of the following:

  • worn or damaged shorting bar or camming beam.
  • the ignition circuit damaged.
  • the RCM disconnected from the vehicle harness.
  • a loss of RCM ground circuits.
  • the RCM inoperative.
  • circuitry.

PINPOINT TEST A: THE AIR BAG WARNING INDICATOR IS ILLUMINATED CONTINUOUSLY - RCM DISCONNECTED, INOPERATIVE, OR LOST/LOW IGNITION FEED

Test Step Result / Action to Take
A1 CHECK FOR CONTINUOUS OR ON-DEMAND SELF TEST DTCs Yes

If continuous DTCs were retrieved, GO to A3 . If on-demand DTCs were retrieved, GO to the Restraints Control Module (RCM) Diagnostic Trouble Code (DTC) Priority Table in this section for pinpoint test direction.

No

GO to A2 .
  • Key in OFF position.
  • Connect the diagnostic tool. Scan Tool
  • Key in ON position.
  • Enter the following diagnostic mode on the diagnostic tool: Retrieve/Clear Continuous DTCs.
  • Retrieve and record any continuous DTCs for use later in this pinpoint test.
  • Enter the following diagnostic mode on the diagnostic tool: On- Demand Self Test.
  • Were any continuous or on-demand self test DTCs retrieved?
A2 CHECK THE RCM CONNECTION Yes

GO to A3 .

No

CONNECT C2041 and engage the locking tabs. GO to A7 .
WARNING: If the supplemental restraint system (SRS) is being serviced, the system must be deactivated and restraint system diagnostic tools must be installed. Refer to Air Bag Supplemental Restraint System (SRS) in this section.

The air bag restraint system diagnostic tools must be removed and the air bag modules reconnected when the system is reactivated to avoid non-deployment in a collision, resulting in possible personal injury.

NOTE: Diagnostics or repairs are not to be performed on a seat equipped with a seat side air bag with the seat in the vehicle. Prior to attempting to diagnose or repair a seat concern when equipped with a seat side air bag, the seat must be removed from the vehicle and the restraint system diagnostic tools must be installed in the seat side air bag electrical connectors. The restraint system diagnostic tools must be removed prior to operating the vehicle over the road.

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

NOTE: After diagnosing or repairing a seat system, 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.

  • Key in OFF position.
  • Deactivate the system. Refer to Air Bag Supplemental Restraint System (SRS) in this section.
  • Key in OFF position.
  • Connect: RCM C2041.
  • Make sure RCM C2041 is fully connected and the red locking tab is engaged.
  • Is RCM C2041 fully connected and are the red locking tabs engaged?
A3 CHECK THE RCM CONNECTOR Yes

CORRECT connector concerns. GO to A7 .

No

GO to A4 .
  • Key in OFF position.
  • Disconnect: RCM C2041.
  • Inspect C2041 component side for a worn, or damaged camming beam. Inspect for foreign material


  • NOTE: The shorting bars can be accessed by prying out the blue cover from the harness side of the connector.
  • Inspect C2041 harness side for worn, damaged, or dislodged shorting bar at pins 20 and 21. Inspect for foreign material.


  • Were any connector concerns found?
A4 CHECK THE IGNITION CIRCUIT 611 (WH/OG) FOR AN OPEN Yes

GO to A5 .

No

REPAIR the circuit. GO to A7 .
  • Key in ON position.
  • Measure the voltage between RCM C2041 pin 2, circuit 611 (WH/OG), harness side and ground.


  • Is the voltage between 9 and 16 volts?
A5 CHECK THE GROUND CIRCUIT 397 (BK/WH) FOR AN OPEN Yes

GO to A6 .

No

REPAIR the circuit. GO to A7
  • Key in OFF position.
  • Measure the resistance between RCM C2041 pin 21, circuit 397 (BK/WH), harness side and a sheet metal ground near the RCM


  • Is the resistance less than 10 ohms?
A6 CHECK CIRCUIT 608 (BK/YE) FOR A SHORT TO GROUND Yes

REPAIR the circuit. GO to A7 .

No

INSTALL a new RCM. GO to A7 .
  • Connect: RCM C2041.
  • Disconnect: Instrument Cluster C220a.
  • Measure the resistance to ground at instrument cluster C220a pin 12, circuit 608 (BK/YE), harness side.


  • Is the resistance less than 10,000 ohms?
A7 CHECK FOR ADDITIONAL DTCs Yes

Do not clear any DTCs until all DTCs have been resolved. GO to the Restraints Control Module (RCM) Diagnostic Trouble Code (DTC) Priority Table in this section for pinpoint test direction.

No

RECONNECT the system.

REACTIVATE the system. PROVE OUT the system.

REFER to Air Bag Supplemental Restraint System (SRS) in this section. CLEAR all DTCs.
  • Refer to the continuous DTCs recorded during Step A1.
  • Were any continuous DTCs retrieved during Step A1?
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