P0420 - Predictably triggered by gas refill

[volvostud]

Still no plugs, this weekend when I do a big service on it. I was however reading another forum post on the P0420 and realized maybe my FRONT o2 sensor is the problem. The detailed code I get says Bank 1, which the other forum was saying is the front sensor. So if that one isn't working right and you get a 0420, then you cannot reliably say if the cat is working or not because you have no reliable pre-cat reading.

So can somebody confirm if the 0420 Efficiency Below Threshold (Bank 1) is speaking to the front or rear sensor?

I assume the front is just a simple replacement (you wouldn't want to spacer the front sensor, right).

[pgill]

Bank 1 is Cylinder 1-3
Bank 2 is Cylinder 4-6

Each Bank has its own catalytic converter and sensors.

The P0420 is set when the time for switching from Rich to Lean and Lean to Rich is too fast.
The Catalytic converter should store some Oxygen and this will result is a delay between the front sensor and the rear sensor detecting the switch.

With that in mind a new sensor might fix your problem and it might make it worse.

I would get the Denso Iridium TT Sparkplugs first.

Good Luck

Paul

[Spaceman23]

It's because you were topping off your gas every fill up. Don't top it off and the evaporative emissions systems and charcoal canister will not get messed up. This ends up creating extra fuel.. instead of vapor.. so at the beginning of your new tank your "vapor" will be liquid fuel. This extra fuel being dumped will make allot more heat in the cat and the down stream o2 or the air/ fuel sensor which ever you have will flip this code. If you do it long enough it will poison the cat and the code will stick. Just let the gas flow slower towards the end of your full and when it clicks off that's it don't keep cramming more fuel in there. On some vehicles it will literally make the gas push out onto the ground or just make it where you're stuck for half an hour at the pump unable to start so usually these owners have adjusted to just not turning the car off while they fill up. But oh well