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Diagnose Multiple DTC Codes: Misfire and IAT/MAF sensors

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Mark S., Jan 30, 2022.

  1. Mark S.

    Mark S. New Member

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    Hello all,
    This is my first time posting to this PRIUSchat and I am relatively new to doing maintenance on my 2010 Prius with 112k miles. Driving home the other day I noticed the check engine light came on. I took it to a car parts store and got the below codes:

    P0304 - cylinder 4 misfire
    P0102 - MAF sensor - circuit low
    P0113 - IAT sensor - high input problem

    Last June I did some maintenance on my Prius for the first time - there seems to be a link unfortunately :(

    Here's what I did:

    Cleaned intake manifold, throttle body, EGR tube, MAF/IAT sensors
    Replaced spark plugs
    Replaced fuel injectors (after market but I used o-rings from original fuel injectors)

    I also recently filled my car up with mid-level gas from Shell before I realized your not supposed to use premium gas for Prius... Any thoughts on how to further diagnose/solve the issue would be so appreciated!

    Thanks,
    Mark
     
    #1 Mark S., Jan 30, 2022
  2. PriusCamper

    PriusCamper Senior Member

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    Check oil level... Check plugs on mass air flow/temp sensor.

    Clear codes and let us know how long it takes for them to return...

    Did you touch the sensors with anything when cleaning or just the spray that's designed for 'em?
     
    #2 PriusCamper, Jan 30, 2022
    Mark S. likes this.
  3. Mark S.

    Mark S. New Member

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    Okay will do- thank you! I didn't touch the sensors with anything other then the cleaner specified in the "Nutz and Bolts" tutorials. Could you explain how the oil level may be causing the problem and how the air flow/temp sensors could be related to the mis-firing? Thanks again
     
    #3 Mark S., Jan 30, 2022
  4. JC91006

    JC91006 Senior Member

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    With many cases of people doing DIY work, sometimes they just don't tighten everything. Since you have a misfire code, I would check if all the plugs are tightly in place. I've seen times where the plugs were not tighten properly and they get damaged/loose as time goes by.

    Why did you replace the fuel injectors on your DIY service? That's not a replacement item on the maintenance schedule.

    The fuel you put into the car has little reasoning behind the misfire code. You could use regular 87, midgrade, or premium fuel in the car. Using anything other than 87 is just paying more, it won't harm the car
     
    #4 JC91006, Jan 31, 2022
    Mark S. likes this.
  5. rjparker

    rjparker Tu Humilde Sirviente

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    Why would work six months ago cause codes a couple of days ago? If it ran fine after the maintenance there is no logical cause and effect.

    Filling up with mid or high grade gas will cause no problems. In fact you might have increased the detergent additives and certainly improved the octane. Both good things. I would run Premium Shell, Chevron or Exxon all the time except for one downside, it lightens your wallet.
     
    #5 rjparker, Jan 31, 2022
  6. Mark S.

    Mark S. New Member

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    I believe the diagnostic codes referenced the exact parts of the car that I replaced or cleaned 6 months ago (i.e. the air flow/temp sensors and the spark plugs/fuel injectors). So it's hard not to make a connection. One code said cylinder 4 misfired so I am wondering if that injector is faulty since it was a cheaper, after market brand.

    I am actually not sure now that I think of it... I was trying to clean all the carbon build-up from the engine/intake and thought replacing fuel injectors was a good idea. Do you think I should re-install the originals? I am wondering if the after market ones I used could be the problem. Double checking connections is also a good idea.
     
    #6 Mark S., Jan 31, 2022
    Last edited by a moderator: Feb 1, 2022
  7. ChapmanF

    ChapmanF Senior Member

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    The mass airflow and intake air temperature sensors are combined in one unit, near the back of the airbox, with one electrical connector to it. That connection and the nearby wiring are probably the first place I'd poke at if I were looking at codes for both sensors.
     
    #7 ChapmanF, Jan 31, 2022
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  8. Mark S.

    Mark S. New Member

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    I purchased a multimeter to investigate the sensors but I am not sure how to physically contact the wires. Do I need to remove the plastic connectors coming from the control unit?
     
    #8 Mark S., Jan 31, 2022
  9. Mark S.

    Mark S. New Member

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    Okay, I've finished todays attempts to work on the car and here's an update:

    1. I tried resetting codes twice by unplugging 12v battery for 15 minute but the engine light never turned off
    2. I tried resetting codes using a code reader but the codes immediately reappeared.
    3. Voltage on the air-flow (MAF) connector was measured on two separate wires at 5 and 11.75 volts
    4. Voltage on the temperature sensor (IAT) connector was measured on two separate wires at 5 and 5 volts

    I believe I need to connect the multimeter to the MAF sensor while it's plugged and with the engine on but I have no idea how to to do this. Please let me know if you have any info on this or can recommend additional things (wiring stuff) to investigate. The more specific the better since I am so new at this!

    -Mark
     
    #9 Mark S., Feb 1, 2022
  10. ChapmanF

    ChapmanF Senior Member

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    You might take a look at this post about successful backprobing.
     
    #10 ChapmanF, Feb 1, 2022
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