Fault Code P0174 anyone help?

[Condor]

I had forgotten that we had a generic fault code reader at home, so plugged it into the S8 this am to see if I could shed some light on the Engine Management Light suddenly coming on - it's given a Fault Code P0174 System too lean Bank 2, whatever that means - could one of the more knowledgeable members give me some info on this and if its serious / expensive / urgent or not?

After three weeks of no success trying to find a local Audi tech, when I realised we had the reader, I thought I'd check and see what it said........

[Nollywood]

Lazy O2 sensor, post-catalyst. Replace, clear code, and all will be well.

[ainarssems]

Originally Posted by Nollywood

Lazy O2 sensor, post-catalyst. Replace, clear code, and all will be well.

I am sorry, I cannot agree- post catalyst O2 sensor only monitors catalyst and would not throw this code but another for catalyst not functioning properly.

This could be pre cat O2 sensor, air/vacuum leak, dirty/faulty injector or cambelt timing off.

[Architex_mA8tey]

16558/P0174 - System Too Lean, Bank 2

Possible Symptoms
Irregular behaviour

Possible Causes
Fuel system
Excessive fuel pressure
Leaking or contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system
Air leaks after the MAF
Vacuum leaks
Improper seated engine oil dipstick
Stuck EGR valve
Oil overfill
Cam timing
Cylinder compression
Exhaust leaks before or near HO2Ss.

Special Notes

Also see: Fuel Trim Info

[Nollywood]

Originally Posted by ainarssems

I am sorry, I cannot agree- post catalyst O2 sensor only monitors catalyst and would not throw this code but another for catalyst not functioning properly.

This could be pre cat O2 sensor, air/vacuum leak, dirty/faulty injector or cambelt timing off.

My guy, no need to be sorry, different opinions. I had the same code on my S8, I cleared the code, but it wouldn't stay off. I replaced a post-catalyst O2 sensor, and that sorted things out.

[Condor]

Are there some things I should check which are relatively simply solved without a lot of mechanical changes?

Like could it be a fuse somewhere?
Clean the MAF sensor unit?
Change air filter?
Generally check hoses as far as possible?

I assume an o2 sensor is a lambda sensor? I did have a fault a few years ago and it was a lambda sensor which was replaced at a main dealers. If I recall it was quite a quick and easy job - is that the case?

I'd like to do as much as possible before going off to some greedy workshop somewhere - when they see a woman with a big ex-expensive car, they generally rub their hands in glee and get ready for a massive rip off

[Sub-Zero]

Leaking and split vacuum hoses mine threw up the same fault code solid engine management light ! Change hoses you will find them split I replaced and cleared the code all okay.

[Condor]

The vacuum hoses have never been changed on my car - if I do them, what part numbers should I be looking for? I was thinking of perhaps changing the hoses, then checking if the code comes back after clearing it, and then changing the MAF and if the fault pops up again after clearing that with the scanner, perhaps having the lambdas done - is that a reasonable route to go?

Are there any fuses I should check as well?

If it still comes back after that then perhaps its a cambelt timing issue and if the price is too high, will need to decide whether or not I should have it done or if I should be getting rid. I've had the car for 7+ years and its the best car I've ever owned - until 2009 it was main dealer serviced, hasn't had a lot of use since then and was laid up for a year under wraps as I had a company car and didn't want to get rid of her, but as I was made redundant a month ago, I reinstalled the battery, booked an MOT which she flew through without even an advisory, but en route home the engine light came on - drives fine, no loss of power, but the idle sounds a bit rough.

Haven't driven her since then - about 3 weeks back - as I was looking for the elusive Ben who is local-ish and had repaired her last year (replaced alternator) just before she was laid up under covers - as I wanted to check what the problem was first. As I've had no luck tracing Ben or getting him to return calls, I remembered I had a code scanner, hence finding the fault code.........

Most of the independents around here seem to be a bunch of sharks or cowboys so I'm nervous of just going to any of them - nor do I intend going to main dealers with a car of this age any longer as its just crazy price time there, too.

So would like to sensibly do whatever I can, or have it done methodicallly........

[ainarssems]

You should get VCDS lead even cheap e-bay one will do and check measuring blocks for MAF values, lambda voltages, fuel trim and misfires and knock sensor voltages before buying new parts. Some of these might point in right direction. In the meantime check vacuum hoses and engine breather hoses.

Are You coming to Christmas meet? Myself or somebody else can have a look at measuring blocks there if You do not buy cable yourself. That's assuming that car run reasonably well and do not misfire.

You can also swap lambda sensor from one side to another to see if fault follows and take out spark plugs to check if they look look running lean or rich.

[Condor]

Finally managed to contact Ben, so hopefully she'll be able to visit him soon. Thanks for all the pointers and advice - will update when I know what's happened in the fuel system!