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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53902
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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2002 Mercedes c240: p0171..p0174 Replaced mass air flow

Customer Question

2002 Mercedes c240: p0171..p0174 Replaced mass air flow sensor replaced vac booster. also replaced one of the two fuel pumps passenger side. I am thinking vacuum leak some where else any thoughts? How much for your advise?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, welcome to Just Answer. My name is***** fault codes can be caused by an intake leak at the manifold. It would have to be at an area that would affect both sides of the motor. The most likely area would be at the throttle body where the air flow meter connects. The best way to find vacuum leaks is with a smoke tester. If you don't have a smoke tester available you can use carb spray to spray around the elbow where it connects to the throttle body and the air flow meter. Another thing to check is the fitment of the air cleaner to the air flow meter. If the air cleaner is not fitted properly it can cause the fault codes. Ideally you should look at the fuel trim values to see if the computer is compensating for an overly lean or an overly rich fuel mixture. A defective air flow meter would not be unusual either. Also, if the fuel adaption values were not reset when replacing the air flow meter the codes may return until the computer readapts.

Let me know if you have any questions. Kindly rate my service when you are done.


Customer: replied 1 year ago.

Hi! I used carb cleaner around vac hoses. Replace ruber gaskets around elbow under maf sensor the were hard as a rock!

Do you recommend I get a some test done?

I still have po171 and 174 codes.
Expert:  Marty replied 1 year ago.

If you are still getting the fault codes I'd suggest the smoke test to locate any vacuum leaks that you may have missed. A fuel pressure test should also be performed. If the codes have been erased and have not returned you may have repaired the problem.

Let me know if you need anything else. Please remember to rate my service in order for the website to credit me for my help.