My 2000 A6 4.2L check engine light came on a while ago and I didn't have time to have it checked, a week and a half later it shuts off. Then it comes on again a few days later then shuts off a week and half later again. This has happened three times now and I'm wondering if anyone else has had this problem before. Based on how I've been driving the problem seems to be dependent on time and not miles. Let me know, thanks.

 

You have to get the fault codes checked, more than likely an emmisions related fault. Faulty gas cap is my best guess.

 

Try to do two things:

1, buy car code reader and eraser (walmart), read the code, and google it, what the code mean. Then erase it.
2, d u fill gas while runing engine? That's also can show up your check engine light.

 

I have had the same problems from time to time, random turn on, some times a few mins, some times a few days
I hate it beacuse there is almost NEVER a problem.....and I keep thinking WTF now!!![:@]

 

From what I understand, the CEL will stay on for a certain number of miles and then extinguish itself if not corrected....unless it's a critical fault in which case the CEL would be blinking. Then after so many miles or time the CEL will come back on.

 

Yes, depending on the car, they will go through a certain # of drive cycles and if the problem is no longer present the light will go out. The CEL only flashes if the car is suspect to catalyst damaging scenarios. If i had to guess by the car, i would say the seconday air injection system has a fault in it.From what I have seen, when they go on and off like that, it is often a diverter valve or leaky hose.

 

I was having the same problem with my 01 4.2 so when I took the car in for other service I told them about it. It was a hassle for them to figure it out since I deleted the code with my own code reader. The code was P0441, Fault in the evap control system purge valve. So they figured out that my purge valve was bad and it was sticking. A fuel system flush (carbon flush, fuelie, the procedure has many names) will also help clean out that gunk. The problerm you descirbed was the exact same one I was having. If I got on the car a little and started driving a lot harder than usual, the light would kick on. Hope this helps...