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CEL FROM AIR BOX?

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I replaced air filter and shortly afterward got a cel and Bank 2 cat code. I was thinking 02 sensor (best case) or a Cat (worst case) but car only has 26k miles.Saw that air intake leak was also shown as one cause. Sure enough I didn't get top of air box on all the way one corner was up. Fixed that, light off with one drive cycle. Why would that cause a cel?
 

Mad Hatter

Gotta go Faster
5,237
4,227
Santiago, Chile
Yes, a leak in the intake will make you run lean and throw a code for sure, but I would think the leak would have to be after the MAF sensor.
 

Grant 302

basic and well known psychic
I'm thinking it changed how air moves over the maf sensor.
I think this is the likely answer. My guess is that the open lid biases the flow to increase the signal over the sensor for a given flow and a rich condition is picked up at the 02 sensor as a bad converter.

The minuscule pressure drop across the filter element compared to unrestricted flow from the open lid might be enough to change the signal on the order of single digit percent or so. MAF signals and tunes are definitely sensitive to that magnitude of change.

I am surprised that it would clear in one drive cycle, but that's a good surprise.
 

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