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Pinpoint Test E: Loud Popping Sound When Cycling The Ignition

WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
  1. E1 CHECK CIRCUIT 1786 (BN/PK) FOR VOLTAGE 
    • Key in OFF position.
    • Disconnect: Starter Relay
    • Disconnect: Audio Unit C240a
    • Key in START position.
    • Measure the voltage between the audio unit, harness side and ground as follows:
      Audio Unit Connector-Pin Circuit
      CD6 C240a-15 1786 (BN/PK)
      All except CD6 C290-3 1786 (BN/PK)
    • Is the voltage greater than 10 volts? 
    1. YES  : If equipped with a subwoofer, go to  E3 . For all others, SEND the audio unit to an authorized audio system repair facility. TEST the system for normal operation after the repair.
    2. NO  : Go to  E2.
  2. E2 CHECK CIRCUIT 1786 (BN/PK) FOR AN OPEN OR SHORT TO GROUND 
    • Key in OFF position.
    • Disconnect: SJB C2280e
    • Measure the resistance between the audio unit, harness side and the SJB, harness side; or between the audio unit, harness side and ground as follows:
      Audio Unit Audio Unit Connector-Pin SJB Connector-Pin Circuit
      CD6 C240a-15 C2280e-17 1786 (BN/PK)
      All except CD6 C290 C2280e-17 1786 (BN/PK)
    • Is the resistance less than 5 ohms between the audio unit and the SJB, and greater than 10,000 ohms between the audio unit and ground? 
    1. YES  : Go to  E5.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  3. E3 CHECK THE AUDIO UNIT 
    • Key in OFF position.
    • Disconnect: Subwoofer Amplifier C466
    • Key in START position.
      • Fig 1: Checking Circuit For Voltage
      GF0025907Courtesy of FORD MOTOR CO.
    • Measure the voltage between the subwoofer amplifier C466-1, circuit 174 (GY/BK), harness side and ground.
    • Is voltage present? 
    1. YES  : Go to  E4.
    2. NO  : REMOVE the subwoofer amplifier. REFER to Subwoofer Amplifier . SEND it to an authorized audio system repair facility. TEST the system for normal operation after the repair.
  4. E4 CHECK CIRCUIT 174 (GY/BK) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Audio Unit C290a
    • Key in START position.
      • Fig 2: Checking Circuit For Voltage
      GF0025907Courtesy of FORD MOTOR CO.
    • Measure the voltage between the subwoofer amplifier C466-1, circuit 174 (GY/BK), harness side and ground.
    • Is any voltage present? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : SEND the audio unit to an authorized audio system repair facility. TEST the system for normal operation after the repair.
  5. E5 CHECK FOR CORRECT SJB OPERATION 
    • Disconnect all the SJB connectors.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect all the SJB connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    1. YES  : INSTALL a new SJB. REFER to MULTIFUNCTION ELECTRONIC MODULES article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR any DTCs. REPEAT the self-test.
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