P0421 & P0431 for years...
 

Hello,

I have a 2003 A4 Q 3.0 that has been throwing these two "Catalytic converter" codes for YEARS. They started well before the odo hit 100k and now that it has 144k, I'm trying to see if it's worth fixing.

Because I'm getting BOTH codes, is that indicative that one or both converters is shot or could it be an O2 sensor?

Any advice is appreciated!

\\Brew

in a high mileage probably the cats. U can always upgrade to hfc with a spacer to see if that rids the cell?

Well I think I started getting the CEL around 75k... my indy simply will "set readiness" before doing my inspection. ;)

I would like to know what this means: upgrade to hfc with a spacer??

Got any DIY type links for me please?

//Brew

Has anyone ever heard of a ECU update from Audi designed specifically to fix the low threshold value? I've been researching this for a while now and I read that someone posted there was a ECU update designed to fix this. If anyone has any information I would GREATLY appreciate it.

I think because the CEL is on, I'm getting terrible gas mileage..

//Brew

Yes Audi does have a ecm upgrade for this problem but I would doubt it would work. The only REAL fix is to replace both cats with factory new units & also replace all 4 o/2 sensors.

I'd first check your plugs to see if they're fouled and replace if they are. If plugs are badly fouled they won't spark properly giving an incomplete burn which leads to premature failure of o2 sensors and cat.

After plugs I'd replace the pre cat sensors and drive for a week and see if fuel economy improved then replace the cats and post cat sensors which would eliminate the engine light.

The reason for leaving the cat and post cat sensors for last are that they don't affect how the car runs. The post cat sensor checks that the cat is filtering properly and don't affect air/fuel ratio; the cat is just a filter protecting the birds and the bees.

With 144k on the clock do you really feel that those sensors should not be replaced? Really!
Those sensors are responsible for telling the ecm how well the cats are working , thus responsible for the fault codes that are present.

High flow Cat. HFC its a replacement for the stock converter that is cheaper then stock but if they are strict on emissions where u live then i would say its a no go.

As of January first 2014 all catalytic converters must be 50 state compliant to be sold in New York.
I stopped using aftermarket cats years ago , they are a temporary band aid at best.

The guy complained of bad fuel economy so its probably the pre cat sensors. The faults been on the dash for years so the faulty cat and sensors should be replaced but I don't think its a high priority that's all

Edit: yeah I was wrong, my logic made sense at the time. Replacing all 4 o2 sensors and cats will rid the fault and should return both power and fuel economy.