clster

Posted a thread earlier about some smaller problems which are now solved but instead I got some bigger ones. I have a 2008 CLS350 CGI with the 292 hp engine. I have had it for 3 weeks.

last sunday I got a check engine light just when I was about to park. I got the car diagnosed with a fairly simple app-connected thing and it said "P0171 - System too lean" The car runs just fine except maybe that it uses a lot of fuel, it has been using more fuel that I thought a 3.5 V6 would. I'm getting 13.0 liters /100km highway some times and 16 in the city... which is V8 SUV territory. And it takes some time to start on the first start of the day.

I am thinking of changing the battery as a first step because it seems bad anyway, after diagnosing the car it wouldn't start... just from standing with ignition for like 10-15 min. But I am hoping someone here may have some suggestions to where I should start if it continues... which it probably will

Plutoe

Tow the car back to the schmuck you bought the car from and request your money back! or tow the car to a local mechanic that works on MB's---This is not a battery issue, much larger!

LexBrett2

You have an air leak somewhere. This can be because a hose is not properly attached or an O2 sensor. This code will not do anything except reduce gas mileage and cause you to fail emissions.

You mentioned you have owned the car 3 weeks? The seller may have cleared the codes, knowing that the error was present, in order to sell the car. How much have you driven the car? It can take a few days of intense driving to go through the drive cycle to get the code to come back after clearing.

Believe me, p0171 is not the end of the world. It won't stop you from getting on the road. If you are a DIYer, this is the type of thing that you can save tons of cash fixing. But figuring out the problem will take time and diligence.

clster

Ok thanks. The check engine came after 2 weeks of ownership and about 1500 km, and after clearing the first time it came back the same day. Then I changed the battery this saturday and cleared it again and it came back this morning. I don't believe he knew about this actually, we know eachother so I don't think he would sell it to me knowing there were faults, he got the car as a trade in though so he have barely used it himslef.

Thats good news if it's the hose or O2 sensor then I guess. I am a sort of semi-DIY. If it's simple and not a great risk of messing something up I'll do it myself but I'm not very much of a mechanic. Where should I start?

clster

Changed one vacuum hose that had a small crack in it and the check engine light has been gone since, but the fuel consumption is still remarkably high...

LexBrett2

OUTSTANDING that you found the leak. Sometimes those little leaks can be near impossible to find, even with a smoke machine.
You call also definitely know if you have a leak by using your OBDII scanner and looking at your "Long Term Fuel Trim (LTFT)". The LTFT is the aggregate of air or fuel added or removed to maintain your optimal air-fuel ratio.
Sounds complicated, but all it means is that if the number is much above 5, then there is a little leak, above 10, a medium leak, above 15 a big leak with a check engine light. Your car will keep running in all circumstances but fuel economy will suck and idle may be affected.

Feel free to private message if you need help!

LexBrett2

Tow a car for a P0171?!
Are you kidding?

clster

Ok, so I might still have a leak somewhere? The car averages about 13 liters/100 km. in speeds around 90 km/h I can get down to 10.5 or 11/ 100 km. I was thinking maybe bad spark plugs?

LexBrett2

First, check your LTFT which is a diagnostic on your scanner. If above 10 there is definitely a leak somewhere.
BUT surely old plugs could be the case.
If not, it is always good to change plugs