Ford Mondeo P0420 Code Symptoms. The P0420 code in a Ford Mondeo will often be thrown if one of your carâs oxygen sensors is not functioning correctly. There are rarely drivability issues associated with P0420. For most people, the first sign that anything is wrong is the service engine soon light coming on.n this guide, I will explain how to remove the standard stereo from a Ford Mondeo MK4. The stereo below is the base stereo, but there are different options available (Sony and Satellite Navigation upgrades). Fitting / removal for listed stereos all have the same procedures, and all connectors across the range are exactly the same (Quadlock).
The fault will lie in the engine wiring loom between the fan and the PCM. (violet wire ) The reason you get 4.44 volts with it dissconnected is the wire isn't loaded /connected therefore the voltage isn't doing any work. Strip this loom back and repair any corroded eiribg that is eveident.
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