footballer96

Hi i recently became the owner of a 2006 ml350, it has about 67000 miles on it and almost right after i started driving the car the check engine light came on, it seemed like it was within 15 mins of getting gas and i thought maybe it was because the gas cap wasnt on tight so i left it alone and it has since been about ten days and its still there and ive refilled the tank. Then yesterday i took it to a shop where they pulled the codes and they got p0171 and p0174. Then they changed the oil and oil filter because that service was due and sent me on my way and i suppose they just cleared the codes, within an hour of driving it returned so after looking it seems to most likely be the mass air flow sensor or the o2 sensors? it seems like the car is driving fine, maybe a little jerk in the transmission but maybe im being overly sensitive, also over the last 500 miles ive only gotten about 15 mpg. Any ideas on what could be wrong and how serious it is would be very helpful! also the seatbelt light seems to randomly come on in the passenger seat without anyone present although i dont think thats related or a big deal. Thanks!

jpcarroll

Those codes indicate a lean condition on cylinder banks 1 & 2. You've likely either got a vacuum leak or the mass air flow sensor needs cleaning/replacing. Lean condition occurs when O2 sensors detect too much air and compensate with extra fuel.

footballer96

Thank you very much. So will driving under those conditions do any damage or should I immediately stop driving it till I take it in, And also is the seatbelt thing just a common nuisance on this car? Thanks again

jpcarroll

Driving with these codes will reduce mileage slightly. If you drive long-term with these codes, your spark plugs will foul. Otherwise, no damage should occur.

Assuming you're not loading any cargo on the front passenger seat to trigger the seatbelt light, it may be a faulty sensor.

madcyborg

after replacing all vacuum lines (the small ones) I had this code still. Then I realized where I got the MAS 6 months before... Walmart, and it was cheap... aha.. So after some debating, I went for the bosch OEM replacement.. $150 and put it on... cleared codes... 300 miles later... No dual P0171/P0174 .. whewww.

Sometimes the replacement parts You use to get back on the road, will turn around to cause more grief... Do it Yourself when You can.. but do it right.