QUALITY MINI CAT LAMBDA FOOLER CAT FOOLER FIESTA ST150 XR4
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The mini cat or "cat fooler" is a small adaptor that has some catalytic platinum substrate inside.
The post cat lambda sensor screws into it.
It basically "fools" the ECU into believing that a catalytic converter is still part of the exhaust system, if the cat has been removed.
It keeps the engine management light off.