I have a 6th gen (4 cylinder, automatic) with about 115k miles on it. The check engine light came on for the first time ever. So I took it to Autozone and had them check it out for free and came back with Code P0420.

The light only came on after my sister drove the car from NJ to NC and back. Never before. Car has no problems at all and still drives perfectly fine. I don't think it's any of the possible causes listed below because the car runs fine without any problems and if it was something like listed below, the car would not be running good. Sine the gas tank was filled a few times on the trip, is it possible to have gotten some bad gas at a station or the maybe someone didn't tighten the gas cap a minimum of 3 clicks and that's what setting off the CEL light?

I haven't reset the light yet because I would like to know what could possibly be setting it off. I think once I go to fill it up again and it still stays on, I'll reset it and see what happens.


I know what the code means...

P0420 67 Catalyst System Efficiency Below Threshold

On the "receipt", they have the definition and explanation of the code, as follows:

Definition - Catalyst Efficiency low-bank 1 (bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank).

Explanation - The oxygen sensors monitor the catalytic converters ability to store oxygen.

Probable Causes:

1. Catalytic converter defective (failure possibly due to #2, 3, or 4)

2. Engine misfire or running condition

3. Large vacuum leak

4. Engine oil leakage into exhaust-valve guide seals, piston rings