I have a Volkswagen Passat GLX, 4-Motion at 95,000 miles. My vehicle has been in for service at the dealership for a persistent check engine light 6 times since June 2006 and the issue has still not been resolved. In June 2006 it was recommended that I have the secondary air pump, 2 combination valves, and the gauges replaced. However, the light came back soon after the repair. At the time of the last service (August 21, 2006) a full inspection was performed and a found the present fault code to be P1423, Secondary Air System Air Flow Too Low, Sporadic Fault. A secondary air test was performed numerous times and each time passed testing. They inspected the valves, lines and pumps and found sealing at this time. They even contacted VW tech support and was instructed to check the charcoal canister and found it to be working as designed and no visable leask were present. At this time, August 30, 2006, my check engine light illuminated while driving. I'm completely frustrated with my vehicle and the dealership. Please...if anyone can assist me and come up some more ideas to assist them in in this repair I would greatly appreciate it! Thanks for reading!

There are alot of things that relate to the secondary air system.
-pump
-combi valves
-Electrical solenoid valve
-relay (most common for "sporadic issues")
-40A fuse
-mass air flow sensor
-front and rear o2 sensors (only used for readiness system test)

At this point they replaced the pump and valves. I would have to think that relay is bad having burnt contacts. The vacuum lines must be ok because you have to remove them to replace the combi valves on he cylinder head.
If the mass air flow sensor is not reading properly it will set a check engine light for secondary air but not very comon. The only time a pump needs to be replaced is if its very noisey (whines when you start the car up for about 30sec to a min). The only reason the combi valves would need to be replaced is if they dont hold vacuum. Looks like the shop just took a stab and installed the most expensive parts (they are the most common to fail though)

From the electronical side, it looks like something is stuck or not working. Germans like to pass multiple lines through components in order to be efficient, it's called--German engineering.

If car drives, I would just do a lot of research before changing anything. And dealers are for selling cars--not fixing them.