Need fast advice on throttle surge on 2016 C

Discussion in 'Prius c Main Forum' started by Absolutely_Red, Sep 16, 2019.

  1. Absolutely_Red

    Joined:
    May 8, 2018
    48
    35
    0
    Location:
    Virginia
    Vehicle:
    2016 Prius c
    Model:
    One
    Today, after driving an hour in 95-degree heat, I discovered that my little red car is surging. When I take my foot off the accelerator, the engine surges dramatically and after 2-5 seconds, slowly comes back down.

    On the interstate, it continued doing 55 mph with my foot OFF the gas for about 5+ seconds.

    It's a terrible sound and I have an appointment with the dealership tomorrow. Please advise.

    Here are the facts:

    *52,200 miles and maintained by the dealership at every service
    *Used only Top Tier gas since it was purchased (at 20,000 miles)
    *There's nothing mechanical obstructing the pedal or its travel.
    *Car mats are where they should be
    *Accelerator pedal springs back and is in good working condition.

    Inspected engine and detected a very heavy burned oil odor coming off the engine. I was unable to remove the oil filler cap because it's too tight (which is odd).

    Found mouse droppings on top of inverter, but no evidence of a nest or chewed wires or any other deterioration.

    Air filter was changed at 45,000 miles. Oil was changed at 50,000. Dealership recommended throttle body cleaning, but when queried, I was told that they just stick a bottle of cleanser in the tank - nothing more.

    I'm beside myself. I'm widowed, alone and bought this car to save some dough.

    Thanks.
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    2,280
    2,151
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    It sounds like it is motoring the engine- meaning, the electric motor is deliberately spinning the gas engine (with no fuel or spark) to bleed off electricity, which can happen when the ECU thinks the battery charge is too high for the current battery temperature. This doesn’t actually indicate a failure per se, just that you’re operating near a temperature limit. You may find that symptoms subside with more air conditioning, since the battery breathes the same cabin air you do.

    Have you cleaned the battery cooling fan? Pop the cover off, clean the grating, then check the foam filter thingy to make sure it isn’t blocked, and lastly pop it off to make sure there isn’t a wad of fuzz stuck in the actual blower itself. Keep it super clean for best battery life.
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    82,295
    35,758
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    any dash lights?

    the throttle body shouldn't need service at 52k, but i'll withhold judgement since something is obviously wrong.

    you definitely don't need a bottle of elixir.

    maybe an egr inspection is in order
     
  4. Absolutely_Red

    Joined:
    May 8, 2018
    48
    35
    0
    Location:
    Virginia
    Vehicle:
    2016 Prius c
    Model:
    One
    No dash lights but I was on the phone and had the a/c off for a few minutes. The car’s interior was broiling.

    I cleaned the screen just three weeks ago and it’s still in beautiful shape.

    Thanks so much for the explanation of the “motoring” of the engine. Where can I learn more about this?

    Btw, once the weather cooled down, the problem disappeared.
     
  5. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    2,280
    2,151
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two

    I can’t remember where I first read about it, sorry. I wouldn’t be surprised if it was in the back of the owners’ manual somewhere, but mine isn’t around to confirm right now. The feature probably has a more official name too, but I don’t know what it is. From your added details it really sounds like that’s all this was.

    The computer will take that step (and some other odd behaviors) to preserve the long term health of the battery. The downside is the annoying noise coming unexpectedly when you’re off-throttle.

    More air conditioning solves the problem two ways- it uses a lot of electricity, so the battery is less likely to top up at stops, and of course it cools the cabin so the battery temperature doesn’t go too high.

    Enjoy the ride!
     
  6. Absolutely_Red

    Joined:
    May 8, 2018
    48
    35
    0
    Location:
    Virginia
    Vehicle:
    2016 Prius c
    Model:
    One
    An update: Took the car in today for oil change and service, and the dealership guy said that if the car hadn't thrown a code, they have no idea how to figure out what's wrong.

    I asked, "If the car threw a code, would the check engine light come on?"

    He said, "Yes."

    The CE light has NOT come on, so I assume there's nothing stored in the on-board diagnostics computer.

    Are my assumptions right?

    BTW, now that cooler weather is here, the problem has stopped. It was only happening on very hot days (90 degrees or more) after the car sat in the heat for a period of time. Now that it's cooled off, it's stopped.

    What a puzzler.
     
  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    2,280
    2,151
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    You're mostly right. The computer can record some conditions without triggering the lamp, but generally these are emissions compliance situations, not 'YOUR CAR IS BROKEN' situations.

    I still don’t think anything was ever actually wrong. The battery was simultaneously too warm and too full for long-term health. The computer solved the problem by partially draining the battery in the most harmless way possible- motoring the engine.

    You can be certain that it had previously tried jacking up the speed of the battery cooling fan, but if the cabin interior was broiling hot then this method would not have been effective, so it tried plan b.
     
    dubit likes this.
  8. Absolutely_Red

    Joined:
    May 8, 2018
    48
    35
    0
    Location:
    Virginia
    Vehicle:
    2016 Prius c
    Model:
    One
    Dear Mr. Leadfoot J. McCoalroller,

    Thank you so much for another helpful post. These explanations have not only been a great help, but they have assuaged my angst. Truly.

    Is there a Mrs. Leadfoot J. McCoalroller? Because any man that knows this much about Toyota hybrids is quite the catch! ;)
     
    dig4dirt likes this.
  9. Matt H

    Matt H Member

    Joined:
    Nov 23, 2012
    150
    83
    0
    Location:
    Okinawa Japan
    Vehicle:
    2012 Aqua
    Model:
    N/A
    The engine flare on stepping off the accelerator is completely normal. We've tried to get to the bottom of it, hours and hours of data logs mapping what the systems are doing, and have never been able to find an answer. They'll do it for a few minutes, and then revert to normal. Best assumption is it has something to do with "battery maintenance," as the battery doesn't charge, nor discharge as quick as it should during these "episodes." Battery SOC, nor temperature plays no part, but in hot environments, it seems to do it more, regardless of battery temperature...

    If you've ever seen the OE service information, there's a lot of [TMG PROPRIETARY INFORMATION] redaction in there, where they dont' want to specify thresholds for this or that. This is one of those situations.
     
Loading...