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Thread: code 171 and 174 but after changing MAF, car idles bad, and light comes back again.

  1. #1
    Join Date
    Feb 2012
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    code 171 and 174 but after changing MAF, car idles bad, and light comes back again.

    '01 catera, about 60k miles, already changed comp for p411, light off for a while, then, came back on,

    code 171 and 174 but after changing MAF, car idles bad, and light comes back again (haven't scan yet)

    any clue?


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  3. #2
    CateraMV6's Avatar
    CateraMV6 is offline Cadillac Owners Connoisseur
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    Turn the Ignition on, but leave engine OFF. Let the car sit for about 5min. It does some sort of idle control valve reset so it may fix your rough idle.

    MAF sensor the one from Saturn at Autozone should fix those codes though.

    It may also be o2 sensors because I had a code for secondary O2 pass side come up a few times car ran like crap until i changed it then it was instantly better.

  4. #3
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    Codes are meaningless without definitions, always list definitions along with codes.

    P0171 and P0174 are lean codes. You have a vacuum leak. Re-check all ducting after the MAF for a proper seal.

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    Submariner409's Avatar
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    liweih21, The MAF was not the problem - there is/was an air (vacuum) leak in either the intake ducting or an EVAP or PCV vacuum feed.

    Does/did the Catera have the built-in code reader/scanner like the Seville/Deville ?

    Go to Seville and read the sticky post "How to pull codes" - you'll also find a link there ("obd2" in the address) that takes you to a Master Index of all P,B,C, and U codes.
    Last edited by Submariner409; 08-09-12 at 06:56 PM.

  6. #5
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    Hi, I end up finding the MAF not aligned correctly, there is this little tab so I aligned and secured it.
    But now, my oil pressure PSI goes all the way up to the left of 80PSI when driving what the heck, before was 25-75max?

    also, where is the intake ducting or an EVAP or PCV vacuum feed?

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    Intake duct - that hose or pipe that connects a remote air filter to the throttlebody. If the MAF is a separate unit (divorced from the throttlebody) any air leak in the intake system at or after the MAF will set mixture codes.

    EVAP system - that system which stores fuel tank vapor in a charcoal canister for burning in the engine intake air mixture during steady cruising speeds. A leak in an EVAP vacuum hose or solenoid hose connector will cause mixture codes.

    PCV system - Positive Crankcase Ventilation system - that calibrated vacuum system which draws clean air through the engine in order to burn evaporated moisture and acid products which condense on the engine interior during cooldown. The clean air pipe usually connects to one valve cover, the vacuum or "dirty air" pipe with PCV valve in line connects to the other valve cover. Any leak in the dirty air line, at or after the PCV, is a vacuum leak and will set mixture codes.

    Check the electrical connector at the oil pressure sending unit.

  8. #7
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    Good info.
    But where is the EVAP and PCV and oil pressure sending unit connections? is there a diagram somewhere?

  9. #8
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    Re: code 171 and 174 but after changing MAF, car idles bad, and light comes back agai

    Hi, update, bought a cheap scanner, saw only code 172 now, what's going on?


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