Thottle sticking on

Check that your floor mats are installed correctly.

 

do you drive with two feet?

i think the potentiometer is in the pedal assembly. climb under and work it with your hand to see if there is any stickiness

 

Yikes! I would call the dealer's response unacceptable and unsafe. Code or not, something's sticking in the throttle area. You might try taking a quick look to see if there's something gumming up the throttle plate, and checking the return spring on the pedal, but the dealer needs to take this seriously.

 

YOU should not have to check anything.
If you had it in a Toyota shop and THEY did not check those things........you need to find a different dealer.

 

but if they did check, and couldn't find anything, i'd park it and call toyota

 

I've never had this happen in my Advanced. That said, most modern electronic throttle control implementations have used two redundant position sensors to correlate the actual position of the pedal, with multiple failure modes with varying levels of functionality (full on limp home, max RPM throttling, etc.)

With that all said I don't have a service manual on this car to confirm further if the logic applies to Prius. All this to suggest that I would guess this is more physical than an electronic issue.

 

+1 to these. Find a shop that takes the problem seriously and avoid driving the car until it’s fixed.

Also, recording a video of the bad behavior might help

 

The symptom suggests an issue with the accelerator pedal and its sensor, not with the actual throttle and its actuator.

You could use the Techstream active data list and watch the two sensor inputs as you smoothly move the pedal to the floor and back up again. Techstream will let you set up a graph of two inputs and save it.

The graph will have weird artifacts (because Techstream is only getting the values by repeatedly polling, it doesn't have the data streaming constantly in) but it might show you something helpful.

I haven't looked at Prime's design specifically, but the typical Prius accelerator sensor is a pair of inputs between zero and five volts, one of which is low with the pedal released and increases with depressing the pedal, while the other is high at rest and decreases. Neither one goes all the way to zero or all the way to five, between the limits of the pedal travel.

 

Did the dealer check only for diagnostic trouble codes—the default when using the Health Check feature of a Toyota Techstream diagnostic system—or did they also check for stored Vehicle Control History events?

These are in two separate data stores, accessed in Techstream under:

• Powertrain / Hybrid Control / Utility / Vehicle Control History
• Body Electrical / SRS Airbag / Utility / Vehicle Control History

That’s right, but the SRS airbag system records a wide variety of events, including “Accelerator signal and brake signal input simultaneously.” The events are described in the Repair Manual (more info), under:

• Engine/Hybrid System: Hybrid/Battery Control: Hybrid Control System: Vehicle Control History
• Vehicle Interior: Supplemental Restraint Systems: Airbag System: Vehicle Control History

That’s how it works on the fourth-generation Prius and Prius Prime, too. New Car Features explains (with some illustrations):

(a) The non-contact type accelerator pedal sensor assembly uses a Hall IC.

(b) The magnetic yoke mounted at the base of the accelerator pedal arm moves around the Hall IC in accordance with the amount of effort applied to the accelerator pedal. The Hall IC converts the changes in the magnetic flux that occur into electrical signals, and outputs them in the form of accelerator pedal effort to the hybrid vehicle control ECU.

(c) This accelerator pedal sensor assembly includes 2 Hall ICs and circuits for the main and sub signals. It converts the accelerator pedal depressed angles into electric signals with two differing characteristics and outputs them to the hybrid vehicle control ECU.​

As @ChapmanF kindly notes above, the problem here is most likely with the accelerator pedal sensor assembly, which is connected to the hybrid vehicle control ECU. If the car was in EV mode, with the gasoline engine stopped, its engine control module and throttle actuator wouldn’t have been involved.

The Repair Manual has an on-vehicle inspection procedure for the sensor assembly to check the voltage readings as the pedal is depressed and released. There is no procedure to inspect or adjust the spring, or indeed to repair any internal components; the sensor assembly, if defective, is replaced as a unit.

Indeed. If it were my car, I’d ask the dealer to open a case with Toyota’s Technical Assistance System (TAS), the dealer-only support line, and provide the case number. Unless TAS could give another convincing explanation and plan for repair, however, I’d insist—as a matter of my own responsibility to others on the road, if nothing else—on having the accelerator pedal sensor assembly (part number 78110-47050, list price $199.80) replaced immediately, with warranty arbitration over the cost later, if necessary.

Parts catalog reference: Figure 78-01, Accelerator Link

 

I suppose a fuel pump could be weak, and not be able to deliver enough fuel. Or a fuel pressure regulator could be going out. Generally speaking, any other cause of poor running/a hard start cold would also cause problems while the engine was warm.

 

As I recall, it took a nasty lawsuit for Toyota to put in that logic. Until they did that, the two could fight each other, one trying to stop the car, the other trying to accelerate it.

 

The braking action generates about 5 times the horspower as the engine, so if drivers actually were pushing the brake pedal, the brake pedal will always win, regardless of any software changes to override the throttle when brake pressed.

The issue came up when some owners rode the brakes and didn't force the car to a stop - they boiled off their brake fluid and lost braking ability.

 

Yikes I am officially spoked best of luck, I am only 401 miles into my ‘20 XLE and I've already screen my mfd show ‘hybrid system failure’ on a cold start up

 

But was there anything at all in the message or the symptoms that made you think you should add on to montreal's thread about a throttle pedal being sticky because of plant material caught in it?

 

twice in 1600 miles is not a lot and in EV mode only narrows it down even more. Do you know how many of those 1600 miles are in EV and how many are in HV and how many km driven between the two times the error message popped up on the MID? Also, do you ever switch into B on the shifter handle?

ChapmanF and Elektroingenieur, do either of you think it's possible that regen could be involved?
I've driven in B mode several times and never had any unusual things happen, but with anomalies like Montreal presents I can't help but wonder what might cause something like that to happen sporadically and how likely the plant material in the grove of the go pedal assembly could be the possible cause.

Montreal, you found the material in the grove and believe it's the possible cause. I'll go take a look around my go pedal and see if I can find the grove you mention on my car. Any other description of the grove and it's location and the amount of material in the grove could be helpful, if you're so inclined to post them.

 

Though as the tragic San Diego CHP Officer crash demonstrated, a decade ago, this wasn't as true on previous generation cars as many people believed. Once the brake booster vacuum supply was depleted, and not replenishable during a stuck WOT event, the non-power-boost brake pedal pressure required to stop high powered cars could become unreasonable. And the NHTSA passenger car braking requirements didn't cover this corner case, covering instead only the easier case of loss of power brake assist while the engine was idling.

Hence the brake-throttle logic lockouts in more recent cars.

 

I was curious at the time why the driver didn't turn the engine off. That should stop the engine immediately unless it was running in compression ignition.

 

That loaner Lexus had push-button ignition, but he was accustomed only to keyed ignition. From passenger 911 traffic, it seems that he stabbed the button many times, but likely didn't know that the emergency shutdown procedure required holding it down for 3-ish seconds, which is an eternity during such an emergency. Toyota has since updated the emergency shutdown in newer designs to recognize and respond to the repeated stabbing method too.

Why he didn't shift the non-hybrid Lexus to Neutral seems to be a mystery. On a Prius, intentionally shifting to N is not instant, but has a delay, about 1-ish second. Long enough to prevent inadvertent shifts, shorter than the power switch delay. I've found that the fastest path to Neutral is to command a shift to Reverse, which at highway speed is instantly overridden by going Neutral with a double-beep warning. Commanding to Park does the same thing, but the Reverse method is much easier to do by feel alone, without taking eyes off the road to find the Park button.

Note to newbies: I have previously described that I have personally experienced (i.e. caused) a Sudden Unintended Acceleration due to pilot error, pedal misapplication, long ago, under extreme fatigue, in a parking lot. But I did it with a manual transmission, and the clutch pedal reflex was one of two things that saved the situation before any damage could happen. That, and the MT driver familiarity with shifting to Neutral, seem to be reasons that manual transmissions are seriously underrepresented (compared to their prevalence) in these sorts of crashes.