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Discussion Starter · #1 ·
My wife's car has come up with this code and I have no idea what to do to fix it. It says, P0420 Catalyst System Efficiency Below Threshold (Bank 1). So what is it saying is wrong or what do I need to fix. I am guessing Bank 1 is refering to the pre-cat O2 sensor?
 

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Re: P0420 Trouble Code - HELP! (Pucks850T)

this code (or one very much like it) just popped up in my audi the other day

all the computer was really saying was that the cat wasnt warmed up when the computer did the cat check. i cleared the code, and checked to make sure everything was running properly, and it hasn't been on since. i have a feeling it was just a freak incident.
 

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Re: P0420 Trouble Code - HELP! (t5p0wer)

How many miles are on the car?

The O2 sensor could be going out, or the CAT could be toast. My bet is the sensor is getting wonky.

I would clear the code and see if it comes back. You won't hurt the car by doing this.
 

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Discussion Starter · #4 ·
Re: P0420 Trouble Code - HELP! (850arrrsaylikepirate)

So I guess I forgot to mention that it has happened twice now. I reset it both times. It hasn't come back on yet, but it only took a few weeks of driving for it to come back. It has around 127,000 I think. So I am guessing it could be O2 or cat, but don't want to fork out the money if I don't have to. Typical scenario with not wanting to shell out more than necessary on these cars.
 

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Re: P0420 Trouble Code - HELP! (Pucks850T)

My '01 has had the same code for a short while now (it comes and goes). I have chosen to ignore for now.

The dealer told me to either replace the CAT or not, it won't hurt anything since the CAT is not broken by their standards. How they checked the CAT I don't know.

My indy shop said its probably an 02 sensor but since the car is running fine to not worry about it till it does.

The indy shop also said that the this code can sometimes been thrown if the motor hasn't been run hard in awhile (carbon build up). So I ran it hard for a few days and the code cleared itself, then after the Wife took her back, the code reappeared.

This could have been just the right timing for the code to disappear, I can't be for sure.

(this was my 666th post... Thank god I am not superstitious, oh wait what's that coming out of the monitor, holy water, I need holy water, stat!!)

Modified by 850arrrsaylikepirate at 9:44 PM 3-16-2009
 

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Re: P0420 Trouble Code - HELP! (Pucks850T)

I just switched out my CAT for a racepipe. I used an O2 spacer but still got this code. Basically the code is telling you that the CAT isn't working properly. If you have a CAT with a lot of miles it is probably bad. If you are running a custom exhaust like I am you may just need an different O2 spacer to fool the sensor.
 
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