I've been getting the codes P01423 and P01411 intermittently (low secondary air flow).
After dealing with this for months I've come to these conclusions:
1. All secondary air components including vacuum hoses are okay. The air pump itself functions regularly.
2. The problem seems to be that the computer controlled secondary air solenoid is only activated intermittently.
Any idea on where I can get information on which sensors etc. the computer relies on in order to determine whether or not to activate the solenoid?
Now that I'm awake let me make some corrections to my original post. The codes are P1423 and P1411...... not p01423 & p01411. Also, the car is a 2000 A6 2.7T (APB).
Also I need to ask ... can anyone tell me where the oil temp sensor is located on this engine? The Bentley manual does not reveal the location. I found the thermal oil level sensor on the bottom of the pan, but I unhooked that and it made no difference on the oil temp gauge which occasionally reads too high.