I put the scanner on the 97 mazda which is having a periodic check engine light situation. It shows P0421 and describes it as "Warm up catalyst efficiency below threshold (bank 1)."
What the hell are we talking about here? Something in the catalytic converter? thanks tom
It's saying the converter is no longer working as well as it should. I would reset it and see if it comes back.
The car you are speaking of has a o2 sensor b4 and after the cat. The one after the cat is called a catalyst efficiency sensor. In your case for some reason yours isn't warming up as specified. Not sure what that means but that is what the deal is. Eli
It's indicating low efficiency detected on the catalytic converter - for this code specifically, it's the pre-catalyst that this vehicle is presumably equipped with to reduce emissions shortly after a cold start.
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