Hi everyone.

Hi have a 99 A6 2.8 v6 quattro Wagon.
I have had it 6 months now. it has around 190000kms on it, in the past few months, the gas mileage has gotten quite bad. I put $30 in which gave me roughly 27 litres. and i only got 160 kms from it. That is very bad. 80 percent of those kms wer highway. I recently changed the purge valve and spark plugs. my check engine light is on but sometime it goes off for a few hours, my central resinator did have to be rewelded because i developed some large cracks in it. i really dont know why the car is so bad on gas now, someone please help me, what is going wrong ?

I read the codes and this is what came up :

-16795 Secondary Air Injection Reaction Injection System incorrect flow
-17544 Long term fuel trim adaptive (Bank 1) system too lean
-17546 long term fuel trim adaptive fuel bank 2
-17708 Misfire Low fuel
-18010 Voltage supply terminal 30 voltage too low
-18032 Request for warning lamp on active

I know U.S cars quite well but these germans are alot more advanced.

Thanks Joe

 

Hi Bombaclad,

It seems to me that based upon the error codes you posted that you may have one or more bad O2 sensors. If your O2 sensors are bad they can be detrimental to your fuel mileage.

 

Why is your voltage at terminal 30 too low?

 

oh ok then, how much do oxygen sensors roughly cost ?

and i dont know why my voltage is too low, i dont know what that thing is.

 

My favorite answer! Check for vacuum leak!

 

All of the suggestions are valid..start checking for warn out vacuum hoses and 02 sensors for starters. The voltage issue is also interesting whatever terminal 30 does but check the other issues first.

 

Watch the votage meter on your dash. With the engine running and the lights on, etc. the voltage may be about 13 or higher. If the voltage drops continuously below 12, then you may need to have the charging system and battery checked.
Low votage on terminal 30 may be causing part of your problem. My Bentley manual does not cover the 1999 Audi, however a low voltage condition may cause false error codes. A vacuum leak may also cause false error codes. So, if you have an older car with several vacuum leaks and a low voltage to the sensors and ECM, then there might be a lot of misleading codes. So, look for broken vacuum hoses, corroded terminals and bad wiring. These are very common on older cars, as are also worn out oxygen sensors.