First post but have been reading the forums for a while. I can't seem to get a straight answer from the dealer or shop so hope someone can help.
Bought a 2002 A6 Quattro 3.0L(AVK) a few years back with about 150K miles on it. After driving it a few days CEL came on, threw two codes: P0421 and P0431. After doing a google search most posts pointed to catalytic converter issues so I called the dealer and they said the parameters are set too tight in that vehicle but everything is fine and if I wanted the light out it would be $2000 a piece to replace the cats. Not good news to hear.
So I put it out of my mind and loved it all summer (never drove/owned an Audi before) until Minnesota winter, then the quattro really made me an Audi convert. All was good until the short commutes (<5mi) made the oil very foamy the color and consistency of butterscotch pudding. (No loss in coolant reservoir). Again the dealer said this is normal with these cars and short trips but I never found a picture with as much foam as I had under the oil filler cap. Eventually froze the PCV and blew the passenger camshaft adjuster seal. Fixed that then heated the car once a week in a shed then took extended drives to try to burn off moisture between oil changes. The next summer my milage kept decreasing and the car has been losing power since. This was the second winter and no oil leaks but I've been very careful to drive at least 10 miles to and from work as well as extended trips. Still getting a lot of foam but I keep an eye on it. The oil smells very gassy as well.
Sorry for the long backstory but my question is:
If the cats are truly bad, would the codes thrown make the car run rich all the time? Would this lead to poor milage and combined with short trips in cold weather overtime cause unburnt fuel to move down piston walls and cause the oil to get very foamy?
I read that both codes constantly on at the same time is almost always bad cats and not O2 sensors. Is this true?
(Quote)If the cats are truly bad, would the codes thrown make the car run rich all the time? Would this lead to poor milage and combined with short trips in cold weather overtime cause unburnt fuel to move down piston walls and cause the oil to get very foamy?
First answer is No, the cat converts unburnt hydrocarbons, the pre O2 sensors adjust fuel trim and the post O2 sensors report the condition of the cats.
Second answer is No, the "tan butter" is moisture in the oil in the crankcase vent system none of this oil would be in the level of the oil pick-up in the pan.
What codes are you getting now?
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