ajg617

This one confuses me. Every time I fill up, the CEL comes on within 5 miles of driving, even if I clear all codes while filling up. And it generates a P0421. This makes me think that I'm dumping more fuel in after a gas fill. That's the only code. Today 3 miles which is just not sufficient to go through the readiness cycles.
Just curious.

GTA_Driver

Usually when you fill up, the only things that can be affected is your EVAP and charcoal canister. It could be the charcoal canister is full of gasoline, but then you'd have an issue w the purge valve.

Cat efficiency is the only code?

GTA_Driver

As a theory, once you open the gas tank cap, it changes the pressure in the system. It's possible that the ECU re-polls all emissions sensors after a change in pressure and that's when the car code is thrown because likely it is dying.

Does the code go away on its own? Or is it always there, unless you clear it?

If the latter, you simply have a low functioning cat, so I don't see what the issue is. Add an O2 spacer and you'll be fine.

ajg617

Yup, only code. Just doesn't make sense to me.

GTA_Driver

It can make total sense, you didn't answer my question, does the code clear itself?

ajg617

Answered your first post - no question on that. CEL no longer goes out on its own - has to be cleared. So failing CAT is likely.

GTA_Driver

Ok. You do have a failing cat.

Wel. You can get new cats $$$

Or install a spacer. Much cheaper.