Hi folks...I'm new to the Audi world with a 2001 A8L, 4.2 Liter, 44K miles. Car is beautiful and runs great but it throws 0171 and 0174 "system too lean" codes. Question is where to head first...oxygen sensors, Mass Air Flow meter, or something else. I figure many of you seasoned veterans out there must have some experience on this.

Also, I have shareware version of Ross-Tech Vag-Com but am pretty new to using it. Can it (or it's fully registered version) actually diagnose this down to the sensor? I'd be willing to lay down the license fee if it does the job.

Thanks for any help...

 

I would first test the fuel pressure and the pressure regulator. You could be loosing pressure.

Test your vacuum lines/system regulator depends on vacuum so does crossover/IMT. If one is cracked replace them all they're cheap www.ecstuning.com has the braided OEM.

Is the problem consistant or come and go.
I would test the ECT, IAT, and MAF as far as sensors. ECT would effect the dash temp gauge, how does that look?

 

The only codes I ever have are 0171 and 0174 ( System too lean, banks 1&2). When I clear codes, they will return within a day or two, especially if I romp in it.

I'm replacing all vacuum lines ('bout half done, but have the difficult ones finished).

 

...and temp guage is rock solid.

 

hes right.. not necessarily a sensor problem, they are probably doing their job.. you have a vacuum leak somewhere is my guess.. if you can look at fuel trims while spraying a can of carb cleaner very carefully along the intake track when your short term trim numbers go way negative then your close to where the vacuum leak is..

 

Just get a barbed splice/ connector and couple the new hose to the old hose and tug them through. I would also change the fuel filter before testing fuel pressure if it is plugged it may be having a hard time keeping pressure.