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Replaced both 02 sensors, still CEL

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Priusoner, Aug 15, 2018.

  1. Priusoner

    Priusoner New Member

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    It all started with my wife complaining of no ooomph or laggy acceleration. I told her these things are not Teslas lol. I drove it and found what she was saying, it was very laggy and sluggish moreso than when we bought it used. It's an 05 with about 120k miles.

    I first cleaned the MAF and some noticiable difference, air filter was clean.

    While I was there, I went ahead and cleaned the throttle body, I removed it actuslly and cleaned that sucker inside out.

    That's where seemingly all the trouble stemmed from as the car was throwing a p0031 code for 02 pre-cat. What a pita, holy God that was an awful exchange. Still throwing a code and rough idle, I went ahead and replaced the sparkies anyway with the recommended iridiums.

    Nothing, still rough idle.

    I replaced the post cat 02 sensors, that was seriously, 5 minute job. The pre-cat ones, more like 5 hour+ lol

    Still running rough idle. I did disconnect battery too....

    What could be the problem? Cats need to be replaced...eeeeek.

    EFI relay, wherever that is and some autozone guy just shrugged his shoulders snd said, worth a shot.

    Anything else I should do?

    Thanks in advance
     
    #1 Priusoner, Aug 15, 2018
  2. Dxta

    Dxta Senior Member

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    You should have first of all, scanned the car for codes before working on em.

    There should maybe be some misfiring codes present, or so.

    Try removing the throttle body assembly, and cleaning it with some injector cleaner.

    Have you checked, and replaced the spark plugs before now? Worn spark plugs would cause sluggishness, as you drive the car.

    Check the fuel injectors for carbon buildups on the orifices of the injectors. If dirty, clean them up by manually removing them from the manifolds, or in some cased, you could introduce a "mechanic in a bottle" product in the fuel tank, and see what happens.

    The EFI relay, does not have anything to do with the condition you're experiencing now.
    If that relay is bad, or the fuse, the car won't start, and the CHECK ENGINE LIGHT won't come on.

    PS: Catalyst is expensive item.
    You got to be sure of it, before replacing em.
    Do you have a P0420 code when you scanned it initially?




    Dxta
     
    #2 Dxta, Aug 15, 2018
  3. Priusoner

    Priusoner New Member

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    Replaces the spark plugs, and I did scan only after cleaning maf and throttle body.

    I havent checked the injectors or used mechanic in a bottle type...what should I use, seafoam?
     
    #3 Priusoner, Aug 15, 2018
  4. Dxta

    Dxta Senior Member

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    You could try that and see what happens. I believe the problem is fuel system related.
     
    #4 Dxta, Aug 15, 2018
    Priusoner likes this.
  5. Priusoner

    Priusoner New Member

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    Okay, thanks, will see if any of that does the trick...
     
    #5 Priusoner, Aug 15, 2018
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The P0031 code means that the heating element for the upstream air/fuel ratio sensor is drawing inadequate current. Hence it could be that the sensor heating element is open, or the wiring harness has a problem, or the EFI M relay (which switches power to that heating element) has dirty switched contacts.

    The EFI M relay is part of the Unit B integrated relay assembly (which contains 4 relays) that has the 15A EFI fuse. That fuse controls power to the EFI M relay.

    After replacing the upstream air/fuel ratio sensor and the downstream O2 sensor, is the check engine light still on? If yes, disconnect the 12V battery for a few minutes to clear the DTC. Then reconnect the battery and see if the engine idle is still rough. If yes, and the CEL light comes back on, have the current DTC read.

    When you removed the throttle body for cleaning, did you use a new gasket between the throttle body and intake manifold, and torque to 15 ft.-lb? Also make sure the clamp between the air filter housing and the throttle body is tight.

    You do not need unmetered air entering the intake, downstream from the mass air flow sensor. That will result in a lean air/fuel mixture and would help explain why you have a poor idle and poor engine power.
     
    #6 Patrick Wong, Aug 15, 2018
    Last edited: Aug 15, 2018
    Priusoner, m.wynn, Dxta and 1 other person like this.
  7. Priusoner

    Priusoner New Member

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    I went back to the throttle body and took another look, I didn't remember the tb gasket and saw that it appeared to be a very thin metal gasket that appeared warped in shape, no silicon rubber ring or anything.

    I found a part at an autoparts store and it was more of those common paper type gasket with a rubber center ring - I replaced that.

    I torqued it down, double checked all the plug-ins from hoses, etc. Above the Throttle body location was a plug in that I can honestly say, if I remembered plugging back in or not so obviously all went back on. Reconnected battery and drove around for a little bit. Maybe not fast enough or that long yet, but code appeared to stay with CEL but red triangle is gone. I think I will continue to drive up some miles - car does run very smoothly once again and no rough idle at slow down or at idle -
     
    #7 Priusoner, Aug 15, 2018
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