Catalytic Converter....Again
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Catalytic Converter....Again
2002 A4 1.8T (135,000 miles) quattro stock.
So about 6 months ago I replaced my cat (after market) and 02 sensors b/c I had the check engine light and couldn't pass inspection. Everything looked normal, passed inspection and car worked perfect. Now the dreaded code is back. What could be causing this?
So about 6 months ago I replaced my cat (after market) and 02 sensors b/c I had the check engine light and couldn't pass inspection. Everything looked normal, passed inspection and car worked perfect. Now the dreaded code is back. What could be causing this?
AudiWorld Super User
Joined: Feb 2010
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From: Fort Worth, Tx
I went through this on an 84 Nissan 300ZX Turbo, so I'll just relay my story.
My Z did not pass emissions about 3 years ago. After assuming it was just the cat, I replaced the cat which becuase it had a new cat and was more efficient, passed the emission test...just barely. I got around to the next year, and I failed the emissions. What I discovered is that my car was running very rich due to a bad o2 sensor which trashed 2 cats. After the o2 replacement, the car passed with a lot of margin. I say this not to point to the o2 senor(s), but to say that you have another underlying problem that is either casuing a rich running condition which will clog your cat or a lean running condition which will degrade the cat due to excessive exhaust heat.
My Z did not pass emissions about 3 years ago. After assuming it was just the cat, I replaced the cat which becuase it had a new cat and was more efficient, passed the emission test...just barely. I got around to the next year, and I failed the emissions. What I discovered is that my car was running very rich due to a bad o2 sensor which trashed 2 cats. After the o2 replacement, the car passed with a lot of margin. I say this not to point to the o2 senor(s), but to say that you have another underlying problem that is either casuing a rich running condition which will clog your cat or a lean running condition which will degrade the cat due to excessive exhaust heat.
Audiworld Junior Member
Joined: May 2010
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I've had this happen to me as well.
Got new CATS and a year later same codes saying the CATS are bad again.
If its just the rear sensor giving CEL codes replace it.
Do a live data capture with a VCDS tool.
Check all the connectors/wires car and cable to the sensor.
I have a 3.0L so I have 2 CATS 2 front and 2 rear sensors.
Aftermarket CATS don't go bad that fast.
Audi/VW's have a LOW tolerance in the emisions area.
Audi has had to back off the emisions setting in the ECU on factory CATS.
So don't think the CATS went bad that fast.
Unless Your engine has other issues that caused it to go bad!
Got new CATS and a year later same codes saying the CATS are bad again.
If its just the rear sensor giving CEL codes replace it.
Do a live data capture with a VCDS tool.
Check all the connectors/wires car and cable to the sensor.
I have a 3.0L so I have 2 CATS 2 front and 2 rear sensors.
Aftermarket CATS don't go bad that fast.
Audi/VW's have a LOW tolerance in the emisions area.
Audi has had to back off the emisions setting in the ECU on factory CATS.
So don't think the CATS went bad that fast.
Unless Your engine has other issues that caused it to go bad!
Last edited by Halo549; Nov 6, 2012 at 04:14 PM.
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