Sudden Unintended Acceleration Events – Prius Gen 3, 2011 Model In Uk

[GreenJuice]

I experienced this for the first time in our Gen 3 last Saturday, then four times yesterday and my wife experienced it once today. I have contacted a local dealer, Jemca Toyota, who have booked the car in for a
‘diagnostics’ check in 12 days time.

I thought it might be important to post my experience here and on Priuschat, in case it happens to others, so that you may know what to expect and also in case others’ experiences can be pooled.

A brief internet search appears to show that the issue of ‘sudden unintended acceleration (SUA)’ in Toyotas and the recalls that took place, seem to have died down or become less reported since 2011. This post is also to record that it *can* still happen now and also to firmly confirm and record the independently witnessed events in my car to be absolutely nothing to do with the floormat interfering with the accelerator pedal!

Background:
Toyota Prius T-Spirit Safety Pack; Registered September 2011 (still within warrantee).
Orders for this model could only be placed for manufacture in Japan, delivery to UK was delayed because of the Tsunami. Very pleased with car. Purchased new with no problems for the last 2.5 years. Full service history with standard annual services completed and no problems.
All events below took place whilst in Eco mode.

I have ScanGauge II installed, so could observe some additional information
during these events. All events with SOC ranging between 45 – 55%.

Sudden unintended acceleration:
1. What it feels like:
The accelerator pedal drops away from your foot. You feel a gentle but firm acceleration as you are pressed into your seat. You can hear ICE revs increasing.
It is NOT like an aggressive ‘foot down’ full acceleration. It is also NOT like a gentle pulling away at lights. It is a firm, definite and insistent acceleration similar to hitting ‘RESUME’ when in cruise control or when you push up the cruise speed by 5 or 10 mph by flicking the cruise lever upwards (except that it is happening at 10 mph on an urban/city road!). It is much faster than normal acceleration in an urban/city traffic. If you do not take immediate and decisive action, a collision will certainly take place (in other words, you know you *have* to act to regain control)

2. How long it lasts:
Approximately 5 seconds. Possibly up to 10 seconds (which is quite long when travelling in traffic!).
SUA is ONLY when ICE is on (i.e., never with MG1/2 driving only). ICE revs are between 1950 and 2100. Watching SGII on one occasion, it terminated as soon as coolant temp hit 60 C (which is a known ICE shutdown temperature on a Gen 3 – therefore, an ICE shutdown control signal can terminate it).

3. Controlling the car:
You can overcome it (easily) by applying the footbrake. You will have to press harder than normal. It is
possible at all times to control the car’s speed and bring it safety to a halt (if you want to). Slipping the car into Neutral will also work. If you go into Neutral when still moving, a yellow triangle appears on the dash display and you get a loud continuous beep alarm. This is a different behaviour to normal. Normally, if you slip the car into Neutral when moving, you do not get this alarm. This alarm can really spook your passengers! After a couple of occasions of this, I decided there was no point spooking my mother-in-law each time, so I just used the foot brake until the car stopped accelerating. I have now done this twice, with my passengers none the wiser that SUA had happened. There is therefore no need to stop the car, you can carry on driving until the SUA event stops by itself. Just stay calm and remain in control. On the observations of a link with ICE activity, I think you can abort the SUA by any method that ‘encourages’ ICE shutdown. Bringing the car to a complete stop will of course do this.

4. More details of each event:

a. April 28, 2014. Second journey of the day. Previous journey 5 hours earlier. Reversed then pulled out of a parallel parked residents bay onto a clear residential road. Reached about 10 mph when I felt SUA which took me up to about 15-20 mph before I reacted (it was my first experience). I held the speed with foot brake then slipped into Neutral. Slowed car down and pulled in to a stop with the alarm and yellow triangle going off. Switched the car off and on again. Everything back to normal for next 5 days.

b. May 1, 2014. Third journey of the day. Previous journey 30 mins before. SUA in stop-start traffic at around 10 mph. Controlled speed with footbrake. Watching SGII in the corner of my eye, saw coolant temp hit 60C, ICE shutdown and the SUA terminated while still moving in Drive.

c. May 1, 2014. Fourth journey of the day. Previous journey 2.5 hours earlier. Three SUA events on this one journey. One event was at 25-30 mph on a moderate incline. SGII showed ICE at 1950 – 2100 RPM. The car maintained its speed on this incline with my feet completely off the pedals as if I was in CC! Final event was after car was in Stage 4 (S4) of engine warm-up cycle (coolant was over 80C and SOC around 50+%).

[i removed the driver’s floormat after this journey, just to prove the point]

d. May 2, 2014. Second journey of the day. Previous journey 1 hour before. Wife was driving this time (she was passenger once before and I had primed her to know what to do). SUA started as she was slowing

down to stop at a junction. Her foot was already on the footbrake, so she just pressed a little harder. As soon as stationary, ICE shutdown as expected and everything was back to normal. I was not in the car. My mother in-law was passenger and witnessed events (a) and (d).

Incidentally, my vehicle was listed under the recent Safety Recall (software fault of the Intelligent Power Module). I received my letter from VOSA about a month ago and thought I could wait till the annual service in the summer, as I have been really busy at work. When I called the dealer about the SUA, I was
informed that this was ‘a separate problem’ and ‘something different’. They would conduct something that sounded like a ‘software flush’ to address the Recall issue at the same visit as this ‘diagnostics’ check. They are also threatening to charge me to pay for insurance cover for the replacement vehicle, but given that the Prius is still under warrantee, I am a member of Club Toyota and am covered by Toyota Motor Insurance, I am going to try and get this negotiated away!

[Grumpy Cabbie]

A copy of my response from Priuschat forum for the benefit of UK owners here;

I had unintended acceleration in my Prius when it was new.

Can you guess what it was? I put a Toyota rubber mat under the Toyota
carpet mat. The carpet mat got under the accelerator pedal and caused
the car to accelerate. This problem has been widely reported and applies
to many cars with that design of accelerator.

That's why Toyota say only to use one set of mats at once and to ensure
they're the official ones for the car and that they're clipped into
place. Use of a loose mat will cause it to slip under the accelerator
(it doesn't have to jam in there) and that causes the car to accelerate.
It was a brown trouser moment as I was in traffic at the time, but it
has never occurred since I clipped the carpet mat down. I left the
rubber mats under the carpet mats in all the other seats (I used the car
as a taxi and you want to protect the carpet).

I'm curious why you felt you had to remove your mat. Why? If it was the
official one, it is no where near the accelerator pedal to even be
considered as a cause. Assuming you have it clipped down? If not, it
doesn't have to slip far under the accelerator to interfere with it.

[GreenJuice]

I'm curious why you felt you had to remove your mat. Why?

Because there we so many web postings that blame the floor mats. I had to completely eliminate this as a possibility.

To be honest, I still can't visualise how a mat lying UNDER the pedal can cause the pedal to depress. Am I missing something?

[Grumpy Cabbie]

I'm curious why you felt you had to remove your mat. Why?

Because there we so many web postings that blame the floor mats. I had to completely eliminate this as a possibility.

To be honest, I still can't visualise how a mat lying UNDER the pedal can cause the pedal to depress. Am I missing something?

Yes. The sensors are UNDER the pedal. The pedal isn't one of those that hangs down like on many cars (this is posted to help others out there as we've already communicated).

[kithmo]

"1. What it feels like: The accelerator pedal drops away from your foot." doesn't this prove that something (e.g. the mat) is pressing the pedal. so it's not a software issue. Either that or it's haunted ;oO

[barrycoll]

The 2013 Gen 3 is a pendant pedal. Just like the brake pedal.

The pedal seems to be inserted into some sort of potentiometer, or fly-by-wire gizmo.....having a second mat under the pedal will make no difference at all, other than stopping the full pedal-to-the-floor movement...

"the pedal dropping away from the foot" seems seriously odd, and almost sounds like the cruise control is cutting in even if not engaged

the dealer's pronouncement will be of great interest..............probably No Fault Found

[GreenJuice]

Thought I should provide an update of comments received on Priuschat.

The pedal movement, that I am convinced I felt, I am now informed could not have happened unless it was physically pushed. Apparently the pedal is simply spring loaded with a Hall effect sensor located at the pivot point. I am informed that there is no actuator or servo mechanism to provide a force feedback, nor a cable as this is all fly-by-wire.

This car has dynamic radar cruise control (DRCC), so in addition to the usual ways that c.c. can accelerate the car, another one is when the car detects the road ahead is clear. I took the car out to the Motorway to test the pedal behaviour in c.c. and can confirm that there was no pedal movement when the car accelerates by itself. Up till then, this was my best guess for the culprit; so now the pedal movement remains the main mystery.

Nevertheless, I do have indisputable and witnessed evidence that the car is not behaving correctly. This is when I shifted to Neutral during the SUA and the alarm went off with the yellow triangle lit. Under normal circumstances if you shift to Neutral when driving, you just slow down. There is no alarm. Hopefully, something might show up on diagnostics, but given the incredulity received to my posts, I suspect Mr T will be the same and I might have to just learn to live with it.

[Grumpy Cabbie]

The 2013 Gen 3 is a pendant pedal. Just like the brake pedal.

The pedal seems to be inserted into some sort of potentiometer, or fly-by-wire gizmo.....having a second mat under the pedal will make no difference at all, other than stopping the full pedal-to-the-floor movement...

"the pedal dropping away from the foot" seems seriously odd, and almost sounds like the cruise control is cutting in even if not engaged

the dealer's pronouncement will be of great interest..............probably No Fault Found

Then give it a go ;)

Put a second mat on top of the official fitted mat and see what happens, but I won't be held responsible.

There is a about half an inch clearance between the floor and the accelerator (depending how far it is depressed). The accelerator has a 'hook' on the back of it, or at least a curcled piece of plastic. The secondary mat blocks the half inch gap and can get hooked on the back of the accelerator holding it in place. If that 'place' is gently accelerating the car, then that's where it stays - gently accelerating. It only takes half a second for a driver to panic in that situation.

So obviously don't try it when driving but certainly have a play around when stationary and see how it is possible if the second mat slips under the accelerator, that it can jam open.

The US dealers have shaved off part of the accelerator to totally avoid the issue. Perhaps Toyota should have allowed a further gap?

[barrycoll]

Had to have a good inspection of the accelerator pedal and mat arrangement, and cannot see that the carpet t can influence anything.....having pulled the carpet right up, I can confirm that there is no sensor mechanism under the carpet, and the pendant pedal is the same arrangement as in my last fly-by-wire Golf....

since the car was new a year ago, I have had a second rubber mat over the carpet, and the rounded bump stop on the accelerator rests on that on excessive pedal movement......unless you dug a hole in the rubber mat, and the pedal caught in that hole, then the accelerator return spring does what it is supposed to do

famous last words, that could bring a proper smile to Cabbies face

[Grumpy Cabbie]

lol I'd never laugh at anybody suffering a stuck accelerator! Brown trouser time if ever there was!

It happened to me. In my earlier post I was wrong, there is not sensor behind the pedal - I was mixing the car up with another. But a double mat does present a problem with the accelerator getting stuck.

In the taxi job it is common to use the thick, heavy duty rubber mats (available at Toyota) to stop wear and tear to your carpets - all those stilettos digging in your carpet wears holes in no time and a hole is a taxi licence fail in my town. You then cover the heavy duty rubber mat with the carpet mat to look nice. The carpet mats would last about 12 months before needing replacement.

My sticking accelerator was caused by using the heavy duty mat in the drivers seat and putting a carpet mat on top. Fine for 99% of the time, but the carpet mat would slip under the accelerator and I'd have to pull it back again. After a while the carpet mats would curl at the edges slightly. I think it was this that caused a problem with mine. The thick rubber mat added with the curled carpet mat was a 'perfect storm' situation.

Since then I quickly removed the rubber mat from my side and just replaced the carpet mats when they got holes in. I also ensured they were no longer loose.

[GreenJuice]

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!

[timberwolf]

Sadly, it is not entirely unexpected when you look at the trouble that owners had in convincing franchised dealers and Toyota that their new Auris HSDs were draining the 12V batteries in 48 hours.

You have a ScanGauge that should be able to read at least part of any DTC thrown?

OTOH if the car is behaving in a way that the engineers had not anticipated then it is possible that there will not be DTC to point directly at an SUA problem.

[GreenJuice]

You have a ScanGauge that should be able to read at least part of any DTC thrown?

Good point. I decided not to use the Scan Tool to check for DTCs *before* taking the car in, just in case it might affect their readings.

I have just checked it now and there are no DTCs but a large number of Pending Trouble Codes (I stopped the process after it got past 65!). So many that I wonder if it might be a feature of Hybrids(?). At a glance, the commonest code is C0CAB and I don't know enough about these to know what they mean.

[Joseph D]

You have a ScanGauge that should be able to read at least part of any DTC thrown?

Good point. I decided not to use the Scan Tool to check for DTCs *before* taking the car in, just in case it might affect their readings.

I have just checked it now and there are no DTCs but a large number of Pending Trouble Codes (I stopped the process after it got past 65!). So many that I wonder if it might be a feature of Hybrids(?). At a glance, the commonest code is C0CAB and I don't know enough about these to know what they mean.

I don't think ScanGauge is useful for anything other that generic ECU faults. You would need to use a Toyota specific reader to pull meaningful codes. I don't know if a code starting with C is a valid DTC for the Prius. DTC codes starting with P, B and U seem to be the most common DTC I've seen.

[Edit] It looks like codes starting with C originate from the ABS system, but nothing with 0CAB.

[steverally]

As Joseph D says code could be associated with ABS.

Is it possible that brakes are being applied for a very short time without any feeling of the car slowing and then releasing such as to give the impression of a sudden acceleration?

[GreenJuice]

As Joseph D says code could be associated with ABS.

Is it possible that brakes are being applied for a very short time without any feeling of the car slowing and then releasing such as to give the impression of a sudden acceleration?

Joseph D, severally,

Thanks for taking the time to respond. I appreciate this as I develop the feeling that most people will be doubting my account of events.

In my fifth event, recorded in '4c' of my original post, the car held it's speed of about 20-25mph going up Muswell Hill (fairly steady incline) without me having any feet on the pedals.

That event stopped, not immediately at the moment of braking near the roundabout at the top of the incline, but when the ICE cut which is just a fraction after applying the brakes.

[timberwolf]

The code could be almost anything, e.g. wheel speed sensors, shifter (joystick), brakes, tyre pressure sensors, intake sensors,... and they are likely to be Toyota and model specific.

Using the shifter to neutral obviously doesn't always cause a yellow triangle and DTC in normal usage. I wonder if it does store a pending code,maybe do it too often and you get a full DTC??

I was a bit surprised that the SGII would show pending codes. I've occasionally run the Scan on my Gen 2 and it always shows No Codes Found.

A pending code usually means an intermittent fault has been detected. What I've read is unclear about what triggers a pending code to match with a later occurrence of the same code and cause a DTC and MIL light to be raised.

[barrycoll]

W's 5th event of climbing Muswell Hill with no driver input sounds serious.....I live at the bottom of Muswell Hill and know that the Prius needs quite a lot of throttle (in Eco mode) to maintain progress...

other than Cruise control cutting in, and then conveniently working at 25 mph, nothing else would allow a zero input climb like that

its a killer on the bike!

[Grumpy Cabbie]

I'm thinking you should up the ante with Toyota. Make a demand. Find out who their press officer is and email them. Give them a time scale OR you'll go to the press. I wouldn't say that was blackmail, just encouragement to take you seriously.

If they're worried about you just playing a game for compo, then just ask for a full replacement car - a swap. They can't argue with that. Alternatively, nobody wants Toyota in the news again for the SUA again, esp Toyota.

[LeeroyJones87]

There's one thing for sure, you should never move the gear lever into neutral whilst the car is still moving as 'coasting' is very dangerous and unnecessary.

I think its very bad that the dealership didn't go on a proper roadtest to try and find any issue you potentially are having.

I think the whole issue of the floor mats is slightly OTT but iv seen mats that have slid under the accelerator pedal cause a few potential issues as it can interfere with the potentiometer.

Sent from my SM-N9005 using Toyota OC mobile app

[GreenJuice]

There's one thing for sure, you should never move the gear lever into neutral whilst the car is still moving as 'coasting' is very dangerous and unnecessary.

Point taken, but worth noting that these hybrids are always in gear as there is no clutch. Putting into Neutral in these hybrids is just an electrical disconnection from the MG1/2 motor/generator. It is undesirable, therefore, also because you can't charge the HV Battery in Neutral and recapture any kinetic energy.

[PeteB]

There's one thing for sure, you should never move the gear lever into neutral whilst the car is still moving as 'coasting' is very dangerous and unnecessary...

Provided it is safe to do so, using N for brief periods can be useful to employ full friction braking, for example to clear rust off the disks when the car's been parked for a while, or when trying to cure squeaky brakes.

Strictly speaking, however, coasting is illegal.

[timberwolf]

It is not against the law, it is only given as advice in the Highway code. e.g. https://www.gov.uk/general-rules-all-drivers-riders-103-to-158/control-of-the-vehicle-117-to-126.

For it to be law in the Highway code, there would a reference in bold text citing the law.

[Grumpy Cabbie]

There's one thing for sure, you should never move the gear lever into neutral whilst the car is still moving as 'coasting' is very dangerous and unnecessary.

Point taken, but worth noting that these hybrids are always in gear as there is no clutch. Putting into Neutral in these hybrids is just an electrical disconnection from the MG1/2 motor/generator. It is undesirable, therefore, also because you can't charge the HV Battery in Neutral and recapture any kinetic energy.

You might want to double check on that. One it's illegal but also putting a hybrid in Neutral at speed doesn't allow any regen (the whole idea behind the hybrid) and also if you're above 45 mph you will be overspinning one of the motors and could cause it to over heat or be damaged. Why? I have absolutely no idea, but I read this on Priuschat where someone asked the very same thing.

Don't use Neutral in a hyrid if you can help it. Doing so at speed for any period can damage the motors and doing so when stationary in traffic stops the engine for firing up if the HV Battery gets too low and this can damage the Battery or worse.

[Joseph D]

... Don't use Neutral in a hyrid if you can help it. Doing so at speed for any period can damage the motors and doing so when stationary in traffic stops the engine for firing up if the HV battery gets too low and this can damage the battery or worse.

One other point to note, if your ICE is running when you stop and you shift into N, the engine will not switch off. And whats more, it will not capture any of the energy back into the HV Battery.