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I changed the fuel pressure sensor and the fuel pump and I got these two codes

Vehicle: BMW 535i xdrive 2009

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Common Causes of P0171 and P0174

1. Vacuum Leaks

This is the most likely cause of too much air being taken into the system. The source of a vacuum leak could be one of many things, including (but not limited to) cracking, wear, or a hole in any of the following:

  • Vacuum hoses
  • Air intake boots (see image example below)
  • PCV hoses
  • EGR valves
  • DISA valves
  • A loose dipstick (or one with a broken seal)

If any of these parts are not forming a perfect seal (have a slit in them) then unmetered air will be entering the engine. Try to listen for a whistle or hiss under the hood with the engine running and visually inspect all hoses and connections.

Example of cracks in an air intake boot causing P0171 and P0174 codes

Example of cracks in an air intake boot causing P0171 and P0174 codes

2. Mass Airflow Sensor (MAF)

The MAF could be under reporting the amount of air passing through the intake. This could be caused by a dirty or fouled MAF or the MAF could be defective also low fuel pressure 

by (125 points)
already resolved thank you for your help was the broken pcv hose and change the intake gasket

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asked Nov 15, 2016 by Lemuel Alfaro (125 points)

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