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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53981
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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got code po 171 & po 174 on 01 mercedez c240 whats poss cause

Customer Question

got code po 171 & po 174 on 01 mercedez c240 whats poss cause
Submitted: 6 years ago.
Category: Mercedes
Expert:  Marty replied 6 years ago.

eurotec :

Hi, those codes are fuel trim codes which indicate that the computer cannot keep the fuel mixture within the proper range. Normally the codes are caused by a bad mass air flow sensor but it is also possible that the codes are caused by a leak in the intake manifold system. The intake system should be smoke tested for vacuum leaks. Those are the two most common causes. Since you've already replaced the mass air flow sensor I suspect you may have an intake leak. Incorrect fuel pressure can also cause the fault code. I'd focus on the intake leaks first and then perform a fuel pressure test if nothing is found.