P0421 code

[littlemoule]

Hi,
I recently got a trouble code. P0421. The fuel injector on bank 1 was changed although the car drives fine. What could be the cause of this and how to fix it?

[Fummins]

P0421 is a catalytic warm up efficiency code.

[littlemoule]

Understood. But why Bank 1? I had some trouble with that before and realized it was a broken/corroded wire to Fuel Injector 1 which was repaired. But I did drive the car like that for quite some time (on just 2 cylinders). Could this have caused the P0421?
What would be a fix for this?

[littlemoule]

[7milesout]

littlemoule - That handheld device seems to be saying that P0421 is 1 of 2 codes stored. There's no mention here about what the other code is / was. Perhaps the other code is regarding the issue with the cylinder misfire.

If the cylinder was misfiring (for quite some time) and dumping fuel in that cylinder that wasn't getting consumed, it's possible the raw fuel being pushed into the catalyst could have degraded the efficiency / lifespan of the catalyst. Hence the P0421.

Just thinking out loud. Not saying I'm correct. I'm wrong a lot, just ask my wife.

[Mitz]

@littlemoule - the Mirage has only 1 bank. The fuel injector you have replaced is on cylinder 1. Bank 1 covers all of the 3 cylinders. Maybe the 2nd of 2 codes can give additional clue of the fault.

The FSM only gives the following as possible causes of P0421



Bank 1 vs. Bank 2: Sensor 1 & 2

[littlemoule]

Here is Code 2 of 2. It says the same thing I think the only difference is it is permanent? Not sure what that means. Ok so mirage has only 1 bank. So likely just the catalytic converter deteriorated since I ran on misfire for some time?

[Wallythacker]

That's what I would guess, catalytic, but what degree of degradation is being tracked? 5%? 15%? 50%?

Can you do a search and find that out? Me, I wouldn't worry if my Mirage told me I had 50% degradation on the catalytic.

[littlemoule]

How do I find out degree of degradation? The handheld tool I borrowed doesn’t report that.

[Fummins]

It's common to have a pending and active code. I see that P0421 code relatively often on higher-ish mileage 2015 Mirages after 300,000km or so. Have the spark plugs ever been changed?
I'm not O2 sensor book learn ed. But from what I understand, the front sensor(pre-cat) is used to adjust fuel/air mixture and the rear o2 sensor is only used to tell if the cat is working properly. The rear O2 sensor normally doesn't affect how the car runs, it's there to tell if you need to pay more carbon tax or not.
I guess a guy could compare the front and rear o2 sensor outputs and if they're similar then your cat is nfg. I dunno, google could probably help out more with that. I don't believe there is a cat degradation value that exists in the ecu?