New sudden unintended acceleration (SUA) events – Prius Gen 3, 2011 model in UK

I slight misunderstanding here, so I apologise if I was not clear. I do not normally have my foot on the gas pedal when adjusting the speed in cruise control. Once cruise is on, I take my foot off and just use the cruise stick on the steering column to go up or down in speed. This is why I couldn't be *sure* if a possible explanation for the pedal movement could lie with the cruise control mechanism.

I did have my foot on the gas pedal for the SUA events when they occurred, and each time the gas pedal distinctly dropped away from my foot.

And this remains an important part of the unexplained puzzle - what could possibly cause the pedal movement?

I went out on the Motorway to test out what happens with DRCC today. The version of cruise control on this car is the Toyota Dynamic Radar Cruise Control. Speed increments are set at 5mph steps for each movement of the Cruise stick. The car will accelerate by itself, without your foot on the gas pedal, in three situations:
1. Setting a higher speed using the stick on the steering column
2. Hitting 'Resume' after braking
3. When locked on the car in front using Dynamic Radar, and the car in front accelerates, or if you pull out into the next lane, with the cruise set at a higher speed. Once the car radar detects the road ahead as clear it will accelerate to the set speed.

For each test, I rested my foot gently on the gas pedal to feel any movement. *There was none*.

Although the third situation was the most difficult to test properly, I think this reasonably eliminates the DRCC as a possible mechanism for pedal movement.

What of the suggestion that the gas pedal is not releasing fully, leading me to think that the car is accelerating?
My historical posts will indicate my interests in hypermiling techniques with assisted instrumentation, firstly with the Gen 2 and now in the Gen 3. Over the years, this does develop a sensitive right foot. If traffic conditions allow, my regular practice for pulling away from a stop situation is to gently get the car rolling on electric only (HSI to the left). This was the situation on that first SUA event. There were no other moving cars on that road. The evidence for acceleration was tactile (I felt being pushed into the seat), auditory (I heard the ICE come on and revs increase) and visual (I saw the speed indicator rise and the RPMs rise on the Scangauge to around 1950 - 2100). I had to control and hold the speed with my foot on the brake, removing the tactile evidence of acceleration, but could still hear and see evidence of the ICE revving, all the time until I pulled in to came to a halt, all the time with my foot on the brake.
Later, I did consider that the car must still have been in S1b of the warmup cycle at that time (coolant temp <40C), but the RPM in that stage (when your foot is off the gas pedal) is around 1280, significantly and noticeably lower. There was a later SUA which took place after S4, which reasonably eliminates the warm-up cycle as a possible link - in other words, it can explain the ICE-on, but not the pedal motion and SUA.

At this time, I have no other ideas of what could explain the gas pedal motion, and would be grateful to receive any.

Thanks for the p.m., it is much appreciated. So far I have been fortunate not to receive criticism, although I am we'll aware that there will be many who would view my post with incredulity and disbelief. If you are in this position, do check out my other posts over several years and you will see that I am not that kind of person.

I did get down, and used a big torch! There was nothing there and also no indication of any kind of 'sensor' under the pedal.

I decided to replace the floor mat, which if your experience is the best explanation so far received, may prompt the SUA event to happen again. I have another eleven days before the car goes in for 'diagnostics' so there is an opportunity for more testing. These photos show the floor mat back in exactly the position when I removed it yesterday - hooked into place and stopping short and well below the bottom of the gas pedal.

You will see that I have a minimalist approach to keeping the car clean and clear of clutter - it helps with hypermiling as well!

I will indeed report back on what they say. If anyone has any ideas on any other tests I could do, let me know.

At the very least, I do have one indisputable and witnessed event that the car was not behaving correctly. For two of the SUA events, I slipped the car from Drive into Neutral and a yellow triangle appeared with a continuous alarm sound. Today, I tested the normal operation of this several times. If you slip the car from Drive to Neutral, you just start slowing down - there is no warning sign and no alarm and this is the normal behaviour.

 

Had to get a front panel beaten out a year ago after someone turned into me when I was stationary at a junction. Low speed scrapes and mysterious dents that appear in supermarket car parks are part of life in London!

 

Thank you. I understand what you say.
As an intermittent problem, I would need something like a GoPro rigged up to do a continuous loop. It won't be easy to prove that my foot was not on the gas pedal at the same time, but capturing the yellow triangle when shifted to Neutral might help. I am kind of getting myself mentally prepared for what you say. In the end, I know I will be completely in their hands and might have to just live with it. If others find themselves in a similar situation, I hope my postings will show that is is OK to keep safe if it happens.

 

OK thanks KBeck. That makes a lot of sense.
If the gas pedal is simply spring loaded, with a sensor at the pivot point, and no servo or actuator to provide any force-feedback then it can only be that the pedal must have been physically pushed.

I can understand why anyone reading this would think 'the OP is a fool'! So I am more than grateful to you for taking the time to respond to my posts!

So I have had my head down there for the last half-hour, tugging at anything loose. There is only the SGII cable shown on the top right of the second photo, which is held with a tie. I even tried changing my shoes to a larger boot to see if my foot could have been catching on anything.

I am left with the unexplained yellow triangle when shifted to Neutral and friendly-jacek's posting that his gas pedal looked different to mine, making me wonder if there might be a unique spec to this car (the 'Safety Pack' option was a bit pricey and perhaps not popular).

Your post has given me some leads and I appreciate that very much.

 

UPDATE:

So the car went in for its ‘diagnostic check’ today. It was always going to have been an interesting day. I just didn’t realise HOW interesting it was going to turn out!


Background:
I spent the last week trying the reproduce the SUA with no success. I even found an old spare car mat and doubled up on the existing mat (secured with cable ties) for a few days just to test out Grumpy’s experience, as he is the only person who has posted an experience like mine.

I also tested out all several situations of shifting from Drive to Neutral to see if I could get the yellow triangle and alarm to come on. Tried it while accelerating briskly, while accelerating in Cruise Control and also with ‘Resume’ on C.C. Same result each time – the car just ‘pips’ once, no alarm and no yellow triangle.

Today, I prepared the car as I always do before a service. I emptied it of all contents; checked the mat again and took a reading on the trip meter, before driving it to Jemca.


At the Garage:
I decided my best strategy was to focus on the problem with the yellow triangle & alarm, which I said happened when I shifted from Drive to Neutral. Then, when asked why I was doing that, I *first* explained that I was an experienced Prius driver who really believes in these cars, but I had experienced some unexpected events and then went on to describe the SUA; including the fact that one of them was experienced by another driver, so not just me. I could sense that this was not going down well....


End of the day:
So I get a call that the car is ready for collection…..

The good news:

a ) they have taken the opportunity to fix the recent recall issue.

b ) all diagnostic checks are clear and they cannot find any problem with the car. (I think we all expected this!)


The bad news:

c ) they tell me that when they found the car, one side of the drivers mat had come off its clip and the whole mat was found rotated and slipped under the accelerator!

You all know from my previous postings how aware I was that the mat is always to be blamed first. The journey to the garage was 4.6 miles. I had checked the mat obsessively over the last 2 weeks *and* before I left the house. There was *no way* I would have left the mat in a position like that, let alone without realising it!


d ) they tell me that they took the car for a good test drive and nothing happened. I checked the reading on the trip meter when I got home. The round trip was 9.2 miles. That test drive would have been less than the measurement error of 0.1 miles!


e ) they then tell me that I should not have shifted the car from Drive to Neutral. They say a ‘senior engineer’ has looked into this and you ‘always’ get an alarm and yellow triangle if you shift to Neutral when driving! They then 'advised' me not to do this again. I said I had been testing this extensively over the previous weeks and then explained what I found normally happens when you do. The service rep said, ‘well I hear you say one thing, by my senior engineer is telling me something else’.


Summary:

So there you have it. Good news is that I can now reassure my mother-in-law that the car has been *fully* tested and there is *nothing* wrong with it (she was a passenger for two of these events, one with me driving, the other when my wife was driving)!

Sad news is that (going in with *absolutely* no intention if picking a fight, and actually asking for help) I now realise what it feels like to come up against Corporate Toyota! They certainly DO NOT want to know!

 

But what if you did conduct that experiment, and regained control by shifting to Neutral?

On testing of my Prius, functioning normally, there is no yellow triangle and no alarm. The triangle and alarm during my SUA events we all witnessed by my passengers - so perhaps here our experiences may differ....


iPhone ?