Rough Idle, Crazy MPG, P0171 & P0496
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Thread: Rough Idle, Crazy MPG, P0171 & P0496

  1. #1
    Driver's Ed MadTownCruiseGirl's Avatar
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    Rough Idle, Crazy MPG, P0171 & P0496

    Certified 2015 1.4T with 49k, purchased in 2016 with 14k. Engine is idling rough & seems to want to stall. CEL came on last Sunday. Ticking noise when running. I had the cruise control on today at 60mph, completely flat road & MPG indicator was erratic - bouncing from 20mpg to 45mpg to 30mpg to 80mpg, etc. AutoZone scan came back with P0171 & P0496. Took it to my usual GM dealer, they want $100 to diagnose & already telling me warranty will likely not cover it. In 9/2017 the water pump went out at 35k (warranty repair). In 12/2017 I had the service interval maintenance including EVAP system inspection & fuel induction service.

    I refused to pay $100 to diagnose when they were telling me it wasn’t going to be covered under warranty based on the codes from AutoZone. I’d rather repair myself. Help!

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    Driver's Ed MadTownCruiseGirl's Avatar
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  4. #3
    Driver's Ed
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    P0496 is for the purge valve and P0171 is for the PCV valve cover. P0171 is very common in Cruze’s

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    Potential causes of a P0496 EVAP code include: Faulty purge or vent solenod/valve Plugged EVAP canister Failed EVAP / fuel pressure sensor Poor electrical connection Short electrical circuit condition (Hyundai, Isuzu) Faulty canister purge valve Blocked vapor canister Faulty vent solenoid Leaking EVAP system hose (Hyundai) Faulty purge flow sensor (Kia, Mazda)

    Read more at: https://www.obd-codes.com/p0496


    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

    Read more at: https://www.obd-codes.com/p0171



    2011-2016 Cruze 1.4 PCV Valve Cover/Intake Manifold Issues



    2011-2016 Cruze 1.4L PCV System Explained


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  7. #5
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    That ticking is the evap purge solenoid, it's attached to the back/top of intake manifold near the firewall. When they fail they get noisy, and set both of these codes.
    P0496 is for the computer seeing evap emissions flow when that solenoid is commanded off. It typically means a mechanical failure of that solenoid.
    Additionally when it fails open like that it is constantly sucking fresh through the emissions system, even at times it's not expected, this extra fresh air cause the P0171 code. There are other common issues that cause it as well, but the solenoid may be covered under your emissions warranty or a special coverage on that part.
    Ask the dealer for a print out of your warranty coverages.

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