RicksS8

Hello,

I have a 2002 D2 S8

I have been having problems with my catalytic converters for around a year now. A muffler shop convinced me to install aftermarket converters when I first started having the problem.

A year later they have failed and said muffler shop will not stand behind their work. I took the car to a local independent mechanic who told me "I have seen this time and time again, aftermarket converters do not work out on Audis or German cars in general, you need to buy converters direct from Audi".

My original converters failed at under 70,000 miles. Has anyone else had this problem? If so, is there a good fix short of buying converters directly from Audi?

Does anyone know who makes Audi's catalytic converters? If so, are they available?

Any help is appreciated,

Rick

silverd2

Please explain "failed"....who decided that? ...what symptom or code indicated "failed"?

RicksS8

The original converters were literally coming apart inside, they were making so much noise that one mechanic I brought the car to (I got three opinions) thought that the engine was knocking.

Fault codes were: 420 & 430

Less than a year later the check engine light started going on again, fault codes are the same as before. I have had two (2) competent shops check for leaks in the system to no avail. Both have said that I am in need of new converters.

twentysevenlitres

So are the catalytic converters rattling, or are you just getting the CEL?

If they're rattling, you need to look at how you're driving. Only some decent hits or splashes through freezing water will consistently crack that ceramic core.

If its the CEL, when was the last time you replaced the O2 sensors?
Faulty rears can give you a bad cat fault.
Faulty fronts can make the car run rich, which long term can coat the core of the cats and cause them to stop doing their thing.

I would also be suspicious of both cats failing at once.

RicksS8

I originally replaced the cats because they were rattling.

12 months later with the new cats I am just getting the CEL.

I have never replaced the O2 sensors but one of the mechanics that I brought the car to fired them with a handheld scanner and said that they checked out fine.

That makes me wonder if they could possibly fail intermittently?

twentysevenlitres

Don't understand? If he scanned the ECU, a bad O2 sensor won't necessarily throw a code.
How do you test them directly? Test the heating element, or testing the sensor for a short doesn't mean the sensor is functioning correctly, or even at its optimum.

RicksS8

I am not sure, the shop that told me they were good tested them all briefly, it could not have been more than a few seconds a piece. He then said that they all "fired correctly".

This happened right before he told me that my converters had gone bad. Is there another test that I should have performed on the o2 sensors?

twentysevenlitres

Well an O2 sensor works by oxygen present in the exhaust generating a voltage across an element. The higher the oxygen content, the higher the voltage.
The ECU detects this voltage and can determine the exact oxygen %.
It only works when the temperature is high, so all modern cars use heated sensors (thus 4 wires - two for the heating element, two for the detection element).

Over time the sensing element loses sensitivity, which effects the ECU's ability to measure O2 % and meter correct fuel quantity. This is why periodic replacement is recommended.

I don't understand how a mech can say "it fired correctly"!!

123quattro

The reason aftermarket cats don't work in an Audi is because the engine controller calibration. The threshold for catalyst efficiency is calibrated pretty tightly and aftermarket cats aren't nearly as high quality as the factory. They new aftermarket units are less efficient to start with so as they lose their catalyzing ability, you'll get the cel much more quickly. Their is no aftermarket source for OE catalysts. I think replacements are about $2500 from Audi.

RicksS8

O2 sensors are relatively cheap so I don't mind replacing them first to see if that is the problem.

If it does turn out to be the cats again does anyone out there have any experience with aftermarket catalytic converter brands on their S8?

If so, what brands were compatible?

$2500 seems like a lot to spend for Audi converters. Especially since my original ones came apart in under 65,000 miles.