Principles of Operation

2009 Ford Fusion SEL, 3.0 1, FWDSECTION Principles of Operation
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.

Standard Audio 

When the audio unit is powered up, audio output signals are sent continuously to the speakers as a fluctuating AC voltage, thus producing sound from the speakers. The steering wheel controls are a multiplexed system that use different resistor values to produce different voltage levels on a single circuit. Each button that is pressed results in a unique voltage signal at the audio unit. This voltage signal is then interpreted by the audio unit as a distinct command. The audio unit has a self-diagnostic mode that can be entered by pressing preset buttons 3 and 6 simultaneously.

Rear Auxiliary Audio Controls 

The rear auxiliary audio controls (if equipped) allow control of certain audio functions by the rear seat passengers. The rear auxiliary controls are located on the top rear of the center console. The signals are sent to the rear audio and temperature control (RATC) module, which sends the signals to the audio unit through the audio corporate protocol (ACP) network.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • You smell fuel, burning insulation, or see smoke.
  • Brakes feel soft, pull hard to one side, or make grinding noises.
  • The engine overheats, stalls repeatedly, or misfires under load.
  • You are missing required tools, torque specs, or safe lifting equipment.
  • You are not confident in the next step or safety outcome.