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Thread: P0171 & P0174 codes.......WTF??

  1. #1

    P0171 & P0174 codes.......WTF??

    OKay, I'm getting the usual P0171/P0174 codes. I pulled & inspected the intake boots & F connector, no cracks. Did a smoke test, didn't see anything. Sprayed the MAF sensor off with solvent too. The car is running fine but those codes keep coming back!!! Any suggestions for where to look next???

    Thanks in advance!

  2. #2
    Quote Originally Posted by OBD-Codes.com
    A code P0171 may mean that one or more of the following has happened:
    The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
    There could be a vacuum leak downstream of the MAF sensor
    Possible cracked vacuum or PCV line/connection
    Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1)
    Sticking/plugged or failed fuel injector
    Low fuel pressure (possible plugged/dirty fuel filter!)
    Exhaust leak between engine and first oxygen sensor
    Since you did a smoke test and cleaned your MAF, we can rule out most of those.

    How many miles on the Oxygen sensors? How many miles on the Fuel Filter?

  3. #3
    I just bought the car a few weeks ago so I can't answer the mileage questions. I'll replace the fuel filter & PCV valve but I thought bad O2 sensors threw their own separate code??

  4. #4
    Join Date
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    Check the PCV system. Its one of the PITA maintenance items that can cause code gremlins. Unless you have documentation that it was recently done, it probably needs replacing.
    Edit: I guess a failed PCV would probably fail a smoke test...
    Last edited by JPMo; 11-28-2020 at 10:03 AM. Reason: clarification

    2004 Titansilber Metallic BMW 330i ZHP

  5. #5
    Quote Originally Posted by JPMo View Post
    Check the PCV system. Its one of the PITA maintenance items that can cause code gremlins. Unless you have documentation that it was recently done, it probably needs replacing.
    Edit: I guess a failed PCV would probably fail a smoke test...
    A failed PCV would not fail a smoke test.

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