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.
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.
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
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.
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!
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.
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.
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!
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.
An update. My little car did this surge again under the same exact conditions as was noted in the original post. We’ve had 95+ degree days here and it’s got to be linked to temperature. Just thought I’d give an update.
Hey I don't know if anybody is still on this thread but I just bought a used 2015 Prius C and my car is doing this too. It's intermittent so it it doesn'tdo it every day. When Im driving and let off gas it revs up and then drops. It does it every time I hit the gas and does it for hours. I do delivery in the car so it is running a lot. It has been hit here lately. But it did do it on a cool day not long ago. I haven't even made my first payment. Please help in very worried I bought a POS car because I've already had to change the water pump I've had the car 4 weeks idk if I should make the payments or just give it back and ruin my credit. I have no regular job right now just doordash and instacart. This is supposed to be temporary til I get another job. I'm also living in this car. It's bad y'all I need help. Call or text me if you can help. 656 263 4584
@AdamBomb77 These cars will motor the engine more than usual when the temperature is high, or if the battery cooling vent is blocked, and also when the hybrid battery is wearing out. Learn to clean the battery cooling vent under the rear left seat. There are youtubes showing how to do it with a vacuum at the carwash. Make sure you keep that area clear to breathe. You should understand that the noise is not harmful to the car. It's just different from most cars, annoying, and you learn to get used to it. Good luck!
I didn't see you mention the miles on the car. The original poster in this thread had a car with such low miles it seemed extra hard to guess what might be happening. But we don't know the miles on yours. The one thing that made me unsure of Leadfoot's diagnosis for the OP's car was one strange symptom: the OP described the car as actually keeping an elevated speed down the road with the go pedal released. That's not the way the well-known "motoring the engine" works; normally, you hear the engine revving higher, but other than that, the car does what you expect. If what your car is doing matches what the cars normally do, then don't worry about it. It is programmed to do that for good reasons.
My car does this if I play with my throttle pedal! It's like the trans has popped into neutral. 90% of the time it's when the battery is at max charge eg: on a downhill run. I tap the throttle and the engine screaams. This is the battery protection trying to prevent overcharging [the energy needs to be dissipated somewhere] If I drive like I'm at the race track [full throttle, then suddenly off the pedal] it sometimes does this. Most of the time it is "Me" telling lies to the management with my right foot. Driving normal with common sense and I never see this happen.
What I'm accustomed to is the reverse of that: the battery is at max charge on a downhill run, and hearing the engine revs increase when I back off the pedal. Give more go pedal and the engine quiets down—because the engine was revving to dissipate energy from slowing the car, and giving more go pedal means less slowing, so less energy to dissipate. I was enjoying that effect on the Midland Trail in WV just this past Tuesday.
This is normal, I get that often if I am riding the brakes [regen] downhill and the battery is fully charged. Normally going downhill in regen the engine is disengaged, If you tap the throttle the clutch engages the motor screams then the clutch will quickly disengage again. By tapping the throttle pedal you're telling the system you want to accelerate. Driving on and off the throttle in rush hour traffic doesn't cause this issue BUT doing this on the Freeway in 65+Mph traffic it will, when the battery is fully charged [the OP's issue] These cars are quite clever, and have an answer to all my bad driving habits [eg: a warning light for my Left-foot trail braking etc]
Where did you get the idea there's a clutch that engages or disengages? Yes, pushing the go pedal further means you want to change the acceleration rate in the positive direction. Things are set up to slightly resist forward motion when your foot is off the pedal (or more than slightly resist, if cruise is on and set for below your current speed). Giving more go pedal first reduces the resistance to forward motion, and then continues adding more power forward. Yes they are.
I was just simplifying the terminology for torque split. On overrun the engine free-wheels through the planetary gears. I've actually tried describing it to my mechanical friends and even they have difficulty under standing the concept I use terms like engage disengage to describe torque split between engine and motor. Technically an electric motor [stator or rotor] controlling speed and torque of a planetary gearset is actually a torque converter even though it behaves like a clutch. My buying motive for these cars was not the Hybrid but purely mechanical reliability of the Toyota E-CVT [compared to those awful belt drive CVTs of other makes.] Apart from Oil, Tyres, a 12v Battery and Fuel my car is 100% reliable
Trying to explain something successfully to others always has been an effective test of how well you understand it yourself. The best resource I've seen around here so far, for the concepts of operation, is the animation Niels Blaauw made back in 2016: Prius Hybrid Drive Explained | PriusChat Prof. Kelly's teardown videos from Weber State University are top-notch for seeing what the actual parts look like and how they go together in real life, but less concerned with developing the concepts of operation. The video by Blaauw instead shows a series of animated models starting with very simple ones, progressing through some physically-unbuildable ones that demonstrate more of the concepts, and finally arriving at a full model (no longer unbuildable) where the concepts have been realized. It's a very effective way of teaching. The problem I've seen with bringing in other familiar things like "clutch" or "torque converter" is they bring in as much that gets in the way of understanding as they bring in that helps. There's really nothing in here that engages or disengages like a "clutch". The only thing that ever can "freewheel" is MG1, and that only when electrical power is neither being supplied to it nor accepted from it. Where people stumble on the terms "torque converter" and "CVT" are that those general concepts have certain specific realizations (fluid coupler with vanes for "torque converter", belts and cones for "CVT") that people nearly always think of first. Once you get past thinking of those specific forms and back out to the most general engineering meaning of a "torque converter" or a "CVT", they end up meaning the same thing, so you could describe the Prius transmission as either. Toyota went with the term CVT, so that's what's most often seen here. Enjoy that while it lasts! It does have some other bits that can wear out, which you can read about on here when needed.
