Ford Mustang (1999-2004) Service Manual: Pinpoint Test M: DTC B1891 - Air Bag Tone Warning Indicator Circuit Shorted to Battery or Ignition

Normal Operation

The restraints control module (RCM) monitors its connection to the generic electronic module (GEM) at pin 10. This connection is used to signal a chime if the air bag indicator is inoperative and another SRS fault exists. If the RCM detects a short to battery or ignition on the connection to the GEM, it will store a diagnostic trouble code (DTC) B1891 in memory.

Possible Causes

An air bag tone warning indicator circuit short to battery or ignition can be caused by:

  • a short to battery or ignition on circuit 1083 (LB/BK).
  • a damaged or inoperative GEM.
  • an RCM internal concern.

PINPOINT TEST M: DTC B1891 - AIR BAG TONE WARNING INDICATOR CIRCUIT SHORTED TO BATTERY OR IGNITION

Test Step Result / Action to Take
M1 CHECK FOR A HARD OR INTERMITTENT DTC 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 M2 .

No

This is an intermittent fault.

The fault condition is not present at this time. GO to M4 .

  • 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.
  • Was DTC B1891 retrieved during the on-demand self test?
M2 CHECK THE AIR BAG TONE WARNING INDICATOR CIRCUIT Yes

GO to M3 .

No

REPAIR the circuit. GO to M5 .

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 the Diagnosis and Testing portion of this section.
  • Key in OFF position.
  • Disconnect: RCM C2041.
  • Disconnect: GEM C201e.
  • Key in ON position.
  • Measure the voltage between RCM C2041 pin 26, circuit 1083 (LB/BK), harness side and ground.

  • Is the voltage less than 0.2 volt?
M3 CHECK THE AIR BAG TONE WARNING INDICATOR Yes

INSTALL a new RCM. GO to M5 .

No

INSTALL a new GEM. GO to M5

  • Key in OFF position.
  • Connect: GEM C201e.
  • Key in ON position.
  • Jumper RCM C2041 pin 26, circuit 1083 (LB/BK), harness side to ground.

  • Does the GEM generate a tone?
M4 CHECK FOR AN INTERMITTENT FAULT Yes

Check for causes of intermittent short to ground or open on circuit 1083 (LB/BK).

Attempt to recreate the hard fault by flexing the wire harness and cycling the ignition key frequently.

REPAIR any intermittent concerns found.

GO to M5 .

No

GO to M5 .

  • Refer to continuous DTCs recorded during Step M1.
  • Was the continuous DTC retrieved during step M1 an intermittent fault?
M5 CHECK FOR ADDITIONAL DTCs YesDo 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 M1.
  • Were any continuous DTCs retrieved during Step M1?
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