I recently got a check engine light on my 2001 A4 Quattro with about 130K miles. I ran the code and it was P0171: Bank 1 System Too Lean.

After doing some reading, it appears that it is either an 02 sensor, MAF sensor or vacuum hose leak around the engine. I replaced my MAF sensor not 5 thousand miles ago, so I'm pretty confident it's not that. Personally I think it's a vacuum hose leak, but I'm not sure how to go about checking for that..

Should I just inspect hoses around the engine while the car is running and listen for a hissing noise or something? I know its easy and cheap to replace them so I'm more than willing to do it myself, in fact I don't want to bring it anywhere because every mechanic I've been to screws me or tries real hard to.

If anyone has any other suggestions as to what might cause this code, I am open to advice. I realize a lot of things can cause a code like this to pop up so I'm not ruling anything out just yet, but I'm pretty confident it's a vacuum hose leak.

Thanks

 

i had the same check engine code.. i first put in the front o2 sensor and that didn't do anything, but after replacing the MAF sensor no more problems and the light hasn't come back on. maybe you got a bad maf sensor the first time.

 

This is more likely an O2 sensor, but checking the other avenues out wouldn't hurt.

 

I'll assume you have a 1.8t. Check the hoses on the left side of the engine for leaks.

 

I have an aftermarket MAFs and an OEM one, which both came with the car. My aftermarket triggers that CEL with that P00171 ODBII code but i get way more boost from it, my engine is also chipped. but i put in my OEM MAFs to pass inspection so check that out if you didnt

 

If you have a 1.8T, check the 3.5mm / 1/8" vacuum line from the intake manifold to the diverter valve, in addition to the more obvious ones. Have a look at the big rubber elbow at the back of the intake manifold -- mine was decomposing from the inside out.

If you cannot find any leaks, the already-suggested O2 sensors and MAF sensor are good bets as well, but obviously costlier to replace.

 

 

Try,

1. Clean MAP sensor (there is a special two can cleaner set at any auto parts store)
2. Check carefully for leaks loose hoses in on and around the manifold with a good light.

Note: listen for a hiss or a whistle sound when you step on accelerator.

Mine had a bad elbow and a vacuum hose that kept coming off. So I would fix it then it would pop off and happen again.

3. Then evaluate test O2 sensor with VAG or similar tool.

 

Hey so i recently bought a 2013 Audi a4 premium quattro with 150k miles and i recently got a check engine light saying my car is running lean on idle and it feels weird kinda like it wants to shut down but not really. I also noticed the light came up when i had a quarter left of gas in the car so i dont know if this has anything to do with it also the car had almost no oil in the car so we filled it up i know sounds like a mess but i want to repair everything this was before the light came up so again i dont know if the oil had anything to do i really dont have that kind of money to buy the MAF sensor or the Oxygen sensor all at once so im really trying to spend only whats needed if you need more answers just reply to me ill answer right away.