A4 Quattro

Check Engine Light Due to Vacuum Leaks, Oxygen Sensor, or Catalytic Converter Fault on Audi A4 Quattro

Problem Description and Possible Solution

Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults can cause the Check Engine Light to illuminate.

Problem Data
RepairPal Verified
Average mileage: 122,299 (45,000–210,000)
Exhaust & Emissions affected: 1.8L 4 Cylinder Turbo
12 model years affected: 1997, 1998, 1999, 2000, more2001, 2002, 2003, 2004, 2005, 2006, 2009, 2011
106 people reported this problem
Viewing 1 - 20 of 36 comments
I have had my check engine light on for last month. The mechanic at the shop put the computer on it and it says bank 1 lean and mis fire on pistons or something like that? The car runs fine but ideals rough.
I first bought the car and noticed that I could smell either exhaust fumes, or burned oil when i would get out of the car. Their was also a rattling noise right underneath the front end of the car. Well the check engine light came on finally and the codes read lean bank 1. I drove it again and a piece fell off underneath and it looks like a muffler or maybe something with the headers or even the catalytic converter. Then the rattling stopped. But after a few minutes of driving, the smell mentioned above got worse. Then I was driving and down a road going about 45 or 50 Mph, and all of a sudden the car started shaking real bad so I pulled of to the side and it felt like i was losing power but I did not and the shaking got worse so I turned it off and now it will not start. It will crankover but wont start.
Vacuum leaks indicated by codes. Dealer and outside mechanics used vapor sniffers to locate a problem but found nothing. After doing my own research, I tried replacing the N80 valve and the problem was fixed. A symptom of a bad N80 valve is that when fueling up the car, the engine will hesitate when starting because of the vapor backup in the failed N80 valve. A replacement can be found for around $25 and installs fairly easy.
Check engine light on. Went to Auto Zone to get a reading and the codes read that it can be a faulty turbo, catalytic converter or an air leak.
I bought this carv2 weeks ago from international auto wholesalers when we test drove it the engine light came on. I spoke to the sales rep and he said they would fix it.they had the car 3 days drove off the lot the engine light came back on and the oil light came on. Called the dealership back they said its a bad sensor. Took it to AutoZone got it scanned and they said it was a faulty catalytic converter and leak/fuel oxygen sensor
my check engine light is on all the time but my vehicle runs good and the comes when the check engine light star blinking my car start chaking alot
check engine light came on - catalytic converter insuffiency - replaced converter and check engine light has come on again after 1,300 miles with new converter. Obd has to be read again. Vehicle seems to be running okay.
The check engine light remains on. Replaced gas cap about 2 years ago. I have worn hose, that probably is leaking air. Not sure how to affect repair myself. The problem seems to be effecting my mileage performance now.
There's not too many details. We bought the car yesterday and last night the check engine light came on. Saturday night meant a quick detour to Auto Zone and the code read for the catalytic converter. We're concerned also that the 75000 mile timing belt was not changed (dealer said the service records were lost and there was now telling). Our efforts to find a solid, used and affordable car seem doomed; it's a pretty grim morning.
I am getting a code PO431- Catalyst Efficiency Below Threshold (Bank 2). I want to know if is the 02 sensor or the actual catalytic converter.
this problem has been an issue for 4 years and 80000 miles even audi couldn't figure it out and just reset computer and I drove to another local garage and they inspected and passed it
It is the Cats, o2 sensors, At $1500 each and $900 for sensors. I was told it is a computer issue and it would be fixed if I got the $1500 Cat done. I had both Cats and the sensors changed , but , not by them and they told me they would flash it for $1500. Car drives fine changed engine for slipped timing belt. Know at least 10 others had the exact issues.
I bought the car used in 2007 and it's been on ever since. We changed the sensor and it's still on. the cluster also has a problem with displaying and we got a 'used' one and still have the same problem. The electrical system must be messed up as the car alarm would go off for no reason. It's ok now. The engine is terrific and handling is great, it loves the road even in 2014 with 144,000 mi on it.