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Discussion Starter · #1 · (Edited)
Restoring an 05 Escape XLT & while conveniently on the jack stands the rear catalytic converter was stolen. I'm in KY where there are no emissions inspections.
With that ...I like to understand how the PCM can tell if the rear catalytic converter exists?
The 1st 2 cats, located off the exhaust manifolds on both sides of the V - Configuration of the engine each have the O2 Sensors which communicate with the PCM. Yet, how does the PCM know the 3rd or Rear catalytic converter is there?
The only thing I can think of is that the down stream O2 sensors sense back pressure from the existence of the rear cat. Yet if that was true wouldn't the downstream O2 Sensors have a different part number for banks 1 & 2 as the back pressure potential would be different at much different distances from the rear cat?
The knowledgeable & accurate input on this site is greatly appreciated.
Thank you
Don - SoLidwire
 

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Expanding just a little, the ECM uses O2 sensors to determine the activity of a catalytic converter. There are no measuring or instrumentation of the 3rd converter, at least for that model year. The other two upstream converters measure the gases before and after the converter has done its work, so would likely by design indicate whether the converter is present and its efficiency or operating characteristics.
tom
 
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