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E-Mission Impossible?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Paul Schenck, Aug 3, 2018.

  1. Paul Schenck

    Paul Schenck Active Member

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    Can a Prius getting 50mpg actually be burning the fuel so poorly that it is non compliant with California emissions?
    I know the O2 sensor is throwing a code P0138 and the light is on so “no pass” though isn’t the performance evidence of exceeding standards?


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    #1 Paul Schenck, Aug 3, 2018
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  2. johnjohnchu

    johnjohnchu Active Member

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    My car was getting 50 mpg while it was burning lots of engine oil internally and had a bad catalytic converter.
     
    #2 johnjohnchu, Aug 3, 2018
  3. Paul Schenck

    Paul Schenck Active Member

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    Yes, I understand how burning enough oil might fail emission or clog a cat,

    If you are adding a quart every two tanks of gas that is 1 quart / 20 gallons. Or 1/80 th or one tablespoon per gallon. One tablespoon per 40 miles will still pass?


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    #3 Paul Schenck, Aug 4, 2018
  4. johnjohnchu

    johnjohnchu Active Member

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    My car was using 1 quart per tank. At that time, the emission test was not required. Eventually I had the engine rebuilt at around 185K miles. Soon after that, the catalytic converter went bad and was replaced. Since then, everything is fine and will reach 300K miles next week. I think the CA emission test may only check to see if there is any DTC code logged. As long as there is no check engine light on, the car probably will pass the test. Of course, I can be wrong. Please correct me if anyone has any additional information.
     
    #4 johnjohnchu, Aug 4, 2018
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    DTC P0138, as you know, means that oxygen sensor downstream from the catalytic converter needs to be replaced. So, just replace it and you will be good.

    That sensor has nothing to do with the fuel economy logged by the Prius. Its purpose is to help the engine ECU determine if the catalytic converter is working properly.

    If the check engine light is on, your car will fail emissions testing, it doesn't matter if you are logging 100 mpg.
     
    #5 Patrick Wong, Aug 4, 2018
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  6. Paul Schenck

    Paul Schenck Active Member

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    I know; If the light is on it will fail.
    My question is can a vehicle that is getting over 40mpg be polluting?

    My first car, a 68 Mercury Cougar XR- 7 390 bored out to 411 c.i. Passed. It got 20mpg on the freeway with a tail wind.
    So it seems to me my Prius on its worst 40mpg day is better than any F-150 getting 20 mpg right?



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    #6 Paul Schenck, Aug 20, 2018
  7. fuzzy1

    fuzzy1 Senior Member

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    Yes, most certainly. Even higher fuel efficiency is possible if NOx limits are exceeded, just ask VW's TDI division. (In the past, that also limited Honda lean-burn engines.) And I can certainly think of ways to exceed CO and HC limits while still getting high efficiency.
     
    #7 fuzzy1, Aug 20, 2018
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  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    That may be true, however compared to the Prius design spec your failing Prius could do better.
     
    #8 Patrick Wong, Aug 20, 2018
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  9. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Absolutely! Keep in mind that street cars just have the bare minimum instrumentation. Nothing on that car can directly measure NOx or hydrocarbon emissions. They're estimated when given data from the things it can measure. Real measurement would have jacked up the price considerably.

    That's part of the logic in the blunt "light on = fail" system. With relatively few sensors to monitor, it doesn't take much in the way of missing or bad data to get the computer to make bad decisions.

    So your MPG reading should be taken as a not-useless sign that it probably isn't polluting more than usual, but it's far from proof.
     
    #9 Leadfoot J. McCoalroller, Aug 20, 2018
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