lucio_liu

same code all the time P0421

I just erased it but it comes back randomly in early morning.
sometimes it just go off for entire month. Good thing is the engine light will not go on soon after I erase it.

Am I going to ignore this code?

lucio_liu

shell 93 v-power helps but sometimes I fill with mobil gas, the light tend to be on. cc seems not bad and MPG is normal

4Driver4

Why not start by looking up the code and posting its meaning?
Including the year and model of your car might help too.

johnkk

16805 - Warm Up Catalyst; Bank 1
P0421 - 35-10 - Efficiency Below Threshold - Intermittent

I get the same thing and just clear the code. You might consider replacing the after cat O2 sensor on the passenger side. A bottle of fuel treatment like techron seems to extend the intervals. I believe one possible cause may be frequent short trips.

GTA_Driver

How old is your car and what is the mileage?

Catalytic converters eventually go on all cars, and yours is not immune from the problem.

The only proper way to fix it is to replace the entire downpipe with the catalytic converters. Not cheap, the part is $1400 from the dealer.

You can also install a spacer for your oxygen sensor, which will get rid of the CEL light and the code. It won't fix your failing cat, needless to say.

Duculescu

I don't know much about cars but we had the same problem a while ago, The Mrs took the car to a garage and they replace some air hose that had a hole in it. Worked like magic so it doesn't need to be anything major.

raj99

based upon the code, I'd look at replacing the O2 sensor...it's pretty straight-forward and not a high-cost fix, if you are somewhat handy

Just Me

Your first step is top know what the code is. otherwise why not just ask "my car broke, what do i do?"

All i did was pop it into my search engine of choice, and the following came back:

http://engine-codes.com/p0421_audi.html

There are several possible problems, the most likely being a bad lambda sensor. Read up.

Nothing will explode.

Grant

lucio_liu

Yes, I google P0421 and it either could be a bad CC or OS.

My audi is 2001 a6, so parts worn out due to the age of use,
but on the other hand, it still runs smoothly.

As long as I can get a 20MPG with a powerful engine, I wouldnt bother to change the OS very soon.

thanks everyone, good thing is I erase the code and the engine light has not been coming on until today. It might comes on a few months later and I will just read it and erase it(if same code)

Just Me

you do knwo a dead O2 sensor can kill a $1000 cat, right?