I have a 2001 Audi A4 (B5) with a 2.8L 30V engine. I purchased the car about a year ago. The car runs good but the check engine light goes on and off a few times a month. I recently purchased a OBD II scanner and the codes read out as follows:
1. P0470- Catylist eff. below threshold (Bank 1)
2. P0173-Fuel trim malfunction (Bank 2)

These were the only codes that poped. I checked the filters as well as hoses and seals to see if there could be an air leak. I have talked to a few mechanics and I still can not reach a conclusion. The car works fine there isn't a rough idle or anything. I was curious what do you think caused these malfunctions? I have done alot of research and there are many different things that could have gone wrong. The most common seems to be an 02 sensor that is bad. I have not replaced any of my 02 sensors and I do not know if I should considering the malfunction light did not pop for them. Also, the 2 different malfunctions occured on different sides. I really do not want to spend over $1000 on a new cat. just to shut off a light (car still passes inspection in my state.) I want to know some opinions on what to check or what I should replace or not.