Drastic Fuel Economy Drop

Discussion in 'Gen 2 Prius Fuel Economy' started by Paige, Aug 5, 2020.

  1. Paige

    Paige Junior Member

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    I have a 2005 Prius with over 200,000 miles on it. I did replace the hybrid battery, 4 years ago.

    Generally, the car was getting 42-47mpg. I do mostly around town driving where it was getting 42, although I haven’t seen 47 in awhile, even on the highway.

    It has suddenly dropped to 37 mph (according to the driver’s screen). And I’m 4 hours away from home. It seems to be running fine and the engine light has not come on. I have changed no driving habits, the only thing that has changed is my mechanic said recently my catalytic converters is bad

    When the battery failed the first time I don’t remember the engine light being on. I just remember the fuel economy dropping drastically and boom! Suddenly it was running VERY badly — and the red triangle came on.

    I checked my tire pressure. All tires are between 30 and 35 psi.

    Is there anything else I should check before I bring it somewhere in a strange town?

    Thanks,
    Paige
     
  2. Paige

    Paige Junior Member

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    After looking at the Fuel Economy questions again I thought I’d add a few things.

    Tires: brand new, bought 3 months ago.
    Alignment: I am not noticing any pull
    Accidents: I did hit a guard rail a month ago, side-swiped it
    12V Battery: Replaced 4 years ago, I think (but not sure). The fuse for the hybrid battery went this spring. Before I towed it to my mechanic, I had friends try to jump it.
    Oil: Had it changed a month ago and they always check the air filter and it was good.
    Brakes: Replaced 2 yrs ago
    Computer Screen (?): shows me getting 99mpg when coasting but when I step on the gas it drops down to 25mpg, even when going slow.
     
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  3. Moving Right Along

    Moving Right Along Senior Member

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    If you replaced the hybrid battery with a used one, the used battery might be nearing its end
     
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  4. dolj

    dolj Senior Member

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    What is the make and model of the tires?
    The minimum tire pressures are Front: 35 PSI; Rear: 33 PSI. Any lower and it will hit your fuel economy.
     
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  5. Paige

    Paige Junior Member

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    Is there any way to tell by looking at the computer screen/monitor with the picture of the battery and wheels showing when engine vs battery are being used?
     
  6. Paige

    Paige Junior Member

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    I was wrong. I bought 2 new tires. They are Solar 4XS. They are in the front. The rear are Cooper Snow Groove. But again, I’ve had these on for months. Why would they suddenly cause a drastic mpg drop?
     
  7. dolj

    dolj Senior Member

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    My guess would be the used battery you bought is nearing the end of its life.
    Prius MDF Energy arrows.jpg

    If the energy flow arrows (labeled 1 in the above image) flow from the engine to the wheels it shows the engine is involved in propelling the car.

    If the energy flow arrows (labeled 4 and 2 in the above image) flow from the battery to the wheels (via the electric motor) it shows the electric motor is involved in propelling the car.

    There can also be a combination of the engine and/or the electric motor to drive the wheels.

    The above image shows the engine is driving the wheels and excess energy (energy flow 3) produced flowing to the motor/generator and then flowing into the battery (energy flow 4).

    There are also more combinations possible and not described here.
     
    #7 dolj, Aug 6, 2020
    Last edited: Aug 6, 2020
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  8. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Hi Paige! What type of hybrid battery replacement did you get?

    also keep in mind a clogged catalytic converter will cause were fuel economy. Unfortunately Connecticut is a CARB state so the replacement would cost a lot. Unlike Tennessee you can get it replaced for a few hundred dollars
     
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  9. Paige

    Paige Junior Member

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    Thank you all for your input!

    On the drive to the dealership, the screen showed the wheels charging on down slopes and the bars went from 6-7. So it was looking pretty good.

    Yes, indeed, the cat is bad, which my home mechanic told me about, but also said it would not affect the performance. He also said the cat converter would be very expensive so he didn’t recommend replacing it given the age and mileage. (Over 200,000.

    The O2 sensor is also bad. Which the dealer mechanic told me, along with the info which I already knew about the cat. Even if they are wrong and there is more issues. I should hopefully be able to get home w/o it crapping out on me!

    Thank you all for your help.
     
  10. bisco

    bisco cookie crumbler

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    can you pass emmisions with a bad cat and sensor?
     
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