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Pinpoint Test C: Loud Popping Sound When Cycling The Ignition Switch

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Audio System for schematic and connector information.

Normal Operation 

When the key is placed in START, voltage is sent to the audio unit through circuit 1000 (RD/BK). When the audio unit receives this signal, it mutes the subwoofer amplifier through circuit 173 (DG/VT). This prevents a voltage surge in the speaker circuits, which could result in a popping noise. After the key is removed from START, the audio unit directs audio signals to the speakers through separate positive and negative circuits.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST C: LOUD POPPING SOUND WHEN CYCLING THE IGNITION SWITCH 

NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  1. C1 CHECK THE RECORDED DTCs 
    • Check the recorded DTCs.
    • Are any DTCs retrieved? 
    1. YES  : For DTC B2913, go to Pinpoint Test D .

      For all others, REFER to DTC Charts .

    2. NO  : Go to  C2.
  2. C2 CHECK CIRCUIT 1000 (RD/BK) FOR VOLTAGE 
    • Key in OFF position.
    • Disconnect: Starter Relay
    • Disconnect: Audio Unit C290a
    • Key in START position.
      • Fig 1: Checking Circuit For Voltage
      GF0018995Courtesy of FORD MOTOR CO.
    • Measure the voltage between the audio unit C290a-15, circuit 1000 (RD/BK), harness side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  C3.
    2. NO  : VERIFY the central junction box (CJB) fuse 3 (10A) is OK. If OK, REPAIR the circuit. TEST the system for normal operation. If not OK, REFER to appropriate SYSTEM WIRING DIAGRAMS article to identify the possible causes of the circuit short.
  3. C3 SUBSTITUTE THE SUBWOOFER AMPLIFIER 
    • Key in OFF position.
    • Connect: Audio Unit C290a
    • Install a known good subwoofer amplifier.
    • Key in ON position.
    • Operate the audio unit in radio tuner (AM/FM) mode.
    • Does the system operate correctly? 
    1. YES  : INSTALL a new subwoofer amplifier. REFER to Subwoofer Amplifier . TEST the system for normal operation.
    2. NO  : INSTALL the original subwoofer amplifier. INSTALL a new audio unit. REFER to Audio Unit . TEST the system for normal operation after the repair.
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