Ford Mustang (1999-2004) Service Manual: Pinpoint Test I: LFC 33/DTC B1933 - Passenger Air Bag Circuit Resistance High

Normal Operation

The restraints control module (RCM) monitors the resistance of the passenger air bag ignitor by measuring the resistance between pins 6 and 7. If the RCM detects high resistance between these pins, it will store a diagnostic trouble code (DTC) B1933 in memory and flash a lamp fault code (LFC) 33 (or higher priority code if one exists) on the air bag indicator.

Possible Causes

A passenger air bag high resistance can be caused by:

  • a poor connection or corrosion in the passenger air bag module circuits.
  • an open circuit or high resistance in the wiring harness.
  • an open circuit or high resistance in the passenger air bag module.
  • an RCM internal concern.

PINPOINT TEST I: LFC 33/DTC B1933 - PASSENGER AIR BAG CIRCUIT RESISTANCE HIGH

Test Step Result / Action to Take
I1 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 I2 .

No

This is an intermittent fault.

The fault condition is not present at this time. GO to I4

  • 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 B1933 retrieved during the on-demand self test?
I2 CHECK THE PASSENGER AIR BAG MODULE Yes

GO to I3 .

No

INSTALL a new passenger air bag module. GO to I5 .

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.
  • Key in ON position.
  • Enter the following diagnostic mode on the diagnostic tool: On- Demand Self Test.
  • Was DTC B1933 retrieved?
I3 CHECK THE PASSENGER AIR BAG MODULE CIRCUIT Yes

REPAIR the circuit (s) as necessary.

GO to I5 .

No

INSTALL a new RCM. GO to I5 .

  • Key in OFF position.
  • Disconnect: RCM C2041.
  • Disconnect: Passenger Air Bag Restraint System Diagnostic Tool.
  • NOTE: By disconnecting the RCM connector, circuit 607 (LB/OG) and circuit 616 (PK/BK) of the RCM connector are shorted together with a shorting bar. Do not remove the shorting bar.
  • NOTE: Zero the multimeter prior to taking the measurement.
  • Measure the resistance between passenger air bag C256, circuit 607 (LB/OG), harness side and passenger air bag C256, circuit 616 (PK/BK), harness side.

  • Is the resistance greater than 0.5 ohm?
I4 CHECK FOR AN INTERMITTENT FAULT Yes

CHECK for causes of intermittent high resistance on circuit 607 (LB/OG) and circuit 616 (PK/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 I5 .

No

GO to I5 .

  • Refer to the continuous DTCs recorded during Step I1.
  • Was the continuous DTC retrieved during Step I1 an intermittent fault?
I5 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 I1.
  • Were any continuous DTCs retrieved during Step I1?
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