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Pinpoint Test I: DTC B2792 - Cross Link Between Firing Loops

WARNING: This page is about a different car, the 2009 Mercury Grand Marquis and 2009 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Police Option for schematic and connector information.

Normal Operation 

The fire suppression system module (FSSM) monitors all of the firing loops circuits for a cross-link (short together) between the circuits of another firing loop. If the FSSM detects a short between the circuits of a firing loop and another firing loop (cross-link), it stores a DTC B2792 in continuous memory and illuminates the fire suppression system indicator.

DTC B2792 (Cross Link Between Firing Loops) - sets when the FSSM detects a short between the circuits of 2 different firing loops (cross-link). This DTC will cause the fire suppression system indicator to illuminate.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST I: DTC B2792 - CROSS LINK BETWEEN FIRING LOOPS 

WARNING: To reduce the risk of accidental deployment, never probe the connectors on the fire suppressors. Failure to follow this instruction may cause unintentional deployment of the suppressors, which may result in serious personal injury.
NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Most faults are due to connector and/or wiring concerns. Carry out a thorough inspection and verification before proceeding with the pinpoint test.
NOTE: The fire suppression system must be fully operational and free of faults before releasing the vehicle to the customer.
  1. I1 CHECK FOR AN ON-DEMAND DTC OR A CONTINUOUS MEMORY DTC 
    • Carry out the FSSM self-test.
    • Was DTC B2792 retrieved as an on-demand DTC during the self-test? 
    1. YES  : Go to  I2.
    2. NO  : CHECK for causes of the intermittent fault. ATTEMPT to recreate the hard fault by flexing the wire harness and cycling the key in the ignition lock cylinder frequently. REPEAT the self-test.
  2. I2 CHECK THE FSSM FOR CROSSLINK BETWEEN #1 FIRING LOOPS 
    • Key in OFF position.
      • WARNING: To reduce the risk of accidental deployment, do not use any memory saver devices when depowering the fire suppression system. Failure to follow this instruction may result in serious personal injury.
    • Disconnect the battery. Refer to BATTERY, MOUNTING & CABLES article.
    • Wait approximately 60 seconds to allow the fire suppression system backup power supply to deplete.
    • Disconnect: FSSM C3281a
    • Measure the resistance between the LH loop and the RH loop FSSM pins, component side, as follows:
      FSSM Connector-Pin (LH Loop) FSSM Connector-Pin (RH Loop)
      C3281a-4 C3281a-12
      C3281a-4 C3281a-13
      C3281a-5 C3281a-12
      C3281a-5 C3281a-13
    • Are the resistances greater than 10,000 ohms? 
    1. YES  : Go to  I3.
    2. NO  : INSTALL a new FSSM. REFER to Fire Suppression System Module (FSSM) . Go to  I6.
  3. I3 CHECK THE BODY HARNESS CIRCUITS FOR CROSSLINK 
    • Connect: FSSM C3281a
    • Disconnect: Inline C339
    • Measure the resistance between the inline C339 pins (LH loop and the RH loop), body harness side as follows:
      Inline Connector-Pin (LH Loop) Inline Connector-Pin (RH Loop)
      C339-3 C339-1
      C339-3 C339-2
      C339-4 C339-1
      C339-4 C339-2
    • Are the resistances greater than 10,000 ohms? 
    1. YES  : Go to  I4.
    2. NO  : REPAIR the circuit(s) in question. CONNECT the inline C339. CONNECT the battery. Go to  I6.
  4. I4 CHECK THE LH FIRE SUPPRESSORS 
    • Connect: Inline C339
    • Disconnect: LH Fire Suppressor C4317
    • Connect the battery.
      • NOTE: DTCs B299A and B299F are expected to be retrieved when the self-test is performed with the LH Fire Suppressor C4317 disconnected. These DTCs can be cleared once all the fire suppression connections are restored. If DTCs B299A or B299F are retrieved with all the fire suppression connections restored, refer to the FIRE SUPPRESSION SYSTEM MODULE (FSSM) DIAGNOSTIC TROUBLE CODE INDEX .
    • Carry out the FSSM self-test.
    • Was DTC B2792 retrieved as an on-demand DTC during the self-test? 
    1. YES  : DISCONNECT the battery. CONNECT the LH fire suppressor C4317. Go to  I5.
    2. NO  : INSTALL a new LH fire suppressor. REFER to Fire Suppressor . Go to  I6.
  5. I5 CHECK THE LH FIRE SUPPRESSORS 
    • Disconnect: RH Fire Suppressor C4317
    • Connect the battery.
      • NOTE: DTCs B29A9 and B29A4 are expected to be retrieved when the self-test is performed with the RH Fire Suppressor C4316 disconnected. These DTCs can be cleared once all the fire suppression connections are restored. If DTCs B29A9 or B29A4 are retrieved with all the fire suppression connections restored, refer to the FIRE SUPPRESSION SYSTEM MODULE (FSSM) DIAGNOSTIC TROUBLE CODE INDEX .
    • Carry out the FSSM self-test.
    • Was DTC B2792 retrieved as an on-demand DTC during the self-test? 
    1. YES  : INSTALL a new fire suppression system harness. Go to  I6.
    2. NO  : INSTALL a new RH fire suppressor. REFER to Fire Suppressor . Go to  I6.
  6. I6 CHECK FOR ADDITIONAL DTCs 
    • Refer to the continuous memory DTCs recorded during Step I1.
    • Were any continuous memory DTCs retrieved during Step I1? 
    1. YES  : REFER to the FIRE SUPPRESSION SYSTEM MODULE (FSSM) DIAGNOSTIC TROUBLE CODE INDEX .
    2. NO  : CLEAR the DTCs. REPEAT the self-test.
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