Help Diagnosing Unintended/Uncommanded Acceleration Issue

I had an older car with a carburetor. The heat stove pipe rotted/fell off in the dead of winter. I noticed it was running a bit rougher than usual, but blamed it on the cold weather

Light turned green, stepped on the gas, all was well. Lights ahead turned red, I lifted my right foot, car kept going. Shifted the auto to N and the engine really raced, so shut the motor off. Pulled over, took the air cleaner off, and the throttle lever was STIFF.

Left it alone a few minutes, and the residual engine heat was enough to melt the ice. Went on my merry way

One thing to keep in mind is that most new vehicles now have electric throttle control, there is no longer any direct connection between the accelerator pedal and the engine. If there is a common defect, say a vulnerability to EMI, we'd be hearing about it by now

Even HD trucks have had electronic throttle control for awhile now. Eg the Detroit Diesel 60 with DDEC IV has had electronic throttle since around 1997. I'm not aware of any semi trucks accelerating out of control but there have been complaints of the pedal going dead and leaving the truck stranded on the side of the road

Toyota has obvously had an issue with floor mats, hence a TSB regarding same. Even with my FJ, the book warns that if the floor mats become unsecured and end up *under* the gas pedal, you could have unintended acceleration or no control over vehicle speed

 

all,

One last consideration for nylion is that it is an '06 with 33,000 miles on it, so he's nearing the end of his bumper-to-bumper factory warranty (I'm guessing only a few months left---he joined in June 2006 & he said he joined before he bought his car). I don't think it's clear if he took the car to the dealer after any of the previous un-intended acceleration incidents (but I would certainly hope that a person experiencing such a serious situation would not just let it go un-checked by the dealer), so there may or may not be any previous record (except for today's dealer visit) for Toyota to consider in the future if this isn't cured for good today & re-surfaces in the future after his warranty is definitely done (usually Toyota has been pretty good about covering a repair that is done after warranty expiration if there have been reports/complaints in the dealer records even if the condition wasn't able to be duplicated to be diagnosed & therefore not repaired at the time of the earlier "in warranty" occurances).

I'm not sure if any of his incidents would throw any codes (although a brake failure one was discussed by one of the responding posters), so the tracking down of the cause(s) of his incidents & the replacement of parts and/or repair could get pretty expensive on nylion's dime after the warranty runs out. Therefore I think it's imperative that his car spend some "quality time" with his dealer if he hasn't been in after the previous incidents (or at least reported them) so they can find a cure before his warranty runs out. And hopefully he may have bought the official Toyota extended warranty which will not only give him longer coverage for the dealer to do more checks (& pay for any work if this condition continues to occur after the factory warranty ends---he still has time to buy that from Troy/Warranty Shack right here on PriusChat for a great, unbeatable price), but it would also provide a free rental car while his is being kept (if longer than 24 hours) unless he has a good dealer who would provide one free out of the goodness of his heart anyways (yeah, not likely). I hope everything turns out successfully.

Ken (in Bolton,Ct)

 

Yes, this sounds like it might be a real instance. nylion, if it happens again without a mat installed, please get it to a dealer within a day to see what trouble codes were created. Good luck!

 

After hearing about 4 ... maybe 5 instances of this ... who knows ... it's not impossible I suppose. I'm sure corporate Toyota is looking into it ... even though we're talking 5 out of a million cars produced. Stats say that's virtually nil. Is it possible the victims were off in la la land? (who among us hasn't been on the phone, only to realize we've driven for miles w/out realizing it). Is it possible some of 'em stomped on the brake instead of the gas? Maybe 1/2 of 'em? When you're talking a million cars ... billions of miles/hours ... stranger things have happened.

 

What I noticed on my Prius (2008) is, that under certain conditions, electric motor boost can quickly "kick in", which results in unintended sudden increase in acceleration. But it was completely controllable. The same millisecond I removed my leg from accelerator pedal, it ceased to accelerate. And of course this was noticeable under low speeds, around 10 to 15 miles per hour, when I was driving on extreme uphill and ICE torque was low (spinning around 2100 rpm).
Probably some fine-tuning to be done in software somewhere not to scare the driver out with extreme electric motor torque.

Ogo

 

The problem described sounds like it could be caused by any mechanism that does not let the accelerator return completely to idle position. Is there anything described that is inconsistent with this?

 

I had that too until I dropped it when I renewed my Geico insurance policy this past February.

What do you think or know about it?

I'm thinking of adding it back in when the Prius' basic 3 years/36,000 miles warranty expires next February.

 

Hi dogfriend,

Good Idea. The partially open throttle would result in a rapid vehicle accelleration after lifting the brake pedal, as the engine would get turned on at that point, and the fuel control would feed the appropriate fuel to match the intake air mass, which would be excessive.

NYLion,
As a shot-gun repair approach, have that the throttle body inspected, cleaned, and the mass sensor cleaned, and also have the engine air filter replaced. Have you ever had the engine air filter replaced? This should be under $150 for this service.

Is that mat out from under the driver's feet yet ???

 

I remember someone reporting something strange happening when their brake light switch had one pole fail. It had some strange effect on cruise control (e.g. cruise control would not turn off or something like that.) Does anyone recall that problem and its effect? From your description, it really sounds like something intermittent mechanically whether it is a switch or throttle, etc. The ECU gets lots of different signals and you could be one of the few cases where the ECU is getting conflicting signals from a hung switch or accelerator hall sensor not fully returning. Read Mike Dimmick's post closely.

It's really outside the dealers expertise to be knowledgeable on every permutation of failure (there are probably over 10,000) so making a real detailed record to send to Toyota USA or even Toyota Japan would actually be a more effective course of action than expecting a dealer to divine an answer with no DTC's. Your offer to instrument the car would certainly identify you as an reasonable driver wanting to resolve a unique problem. The dealers are definitely not set up to do that and have few options other than to admit their limitations.

 

Ok.

You live in a world where calling a person a troll is not a personal attack???

 

nylion, after re-reading the thread I want to be very clear on something: was the car accelerating (that is, moving and increasing speed)? Or was the engine revving up without accelerating the car?

 

You've given us a lot to think about and I'm glad you understand the problem intermittent ("edge") problems. Most of all, I appreciate a commitment to chasing this to ground ... even if unexpected.

In the NHW11, the hybrid vehicle ECU commands a power level to the engine ECU that handles the throttle and other engine systems. So again, we're back to the common element, the hybrid vehicle ECU. Hummm.

Now I've only seen one NHW20 accelerator but I remember the pedal is mounted on a "U" channel but I don't remember if it is closed on the bottom. Perhaps some of the other NHW20 owners can confirm this? I'm posting about the lever the pedal is mounted on. In contrast, the NHW11 pedal is mounted on a solid rod.

I don't like to suggest an untestable hypothesis but I would probably look very closely at the surface of the mat under the accelerator. In particular, I would bend it back just to see if there is any evidence of a crack or slot ... But again, I've only seen an NHW20 accelerator assembly once and only briefly.

A wild thought, would you consider putting a layer of aluminum foil on the upper right part of the mat, possibly held with duct tape, just under the accelerator? The goal is to see any pedal impression in the foil. This provides empirical evidence of whether or not the accelerator pedal was reaching the mat ... without drawing any conclusion. This is just a passive approach to help eliminate one hypothesis. In the case of the NHW11, the pedal assembly has a mechanical stop so the pedal arm can never reach the floor with any appreciable force. But there is not a whole lot of space between the pedal and the carpet.

The bad news is I have always found that without some corrective action, even 'shotgunning', intermittent problems will come back. The good news is this thread is beginning to address things to check. I'm sending a note to the moderators suggesting this thread might do with a more helpful subject line, "Diagnosing Unexpected Acceleration," which reflects the current tone.

One other thought, there is a separate communication network that goes from the hybrid vehicle ECU to the engine ECU. I don't know enough about the protocol (aka., is there a CRC?) but if there were a 'noisy' connector (the bane of my existence,) reseating the hybrid vehicle ECU and engine ECU connectors would make a lot of sense.

Have you gotten a vehicle repair manual? Avoid the Chiltons sold at the car repair places ... I got one and it was nearly useless. There are reports of a better one Bentleys(?) that may have more details.

A better answer may be to check Ebay for 2004-2009 repair manuals, $100-300, (unless you prefer electronic manuals.) They are a valuable roadmap to understanding your car's systems.

For grins some day, try the "forced charge:"

• Hold brake, hard
• Floor accelerator
• Watch battery SOC - this is an under documented procedure that I too was skeptical about. The engine will run putting a charge on the battery, typically 5-10 minutes, until it reaches 80%. Then the engine will shutoff. I don't recommend it as a regular practice but knowing about it and a short test, say 1-2 minutes, is enough to 'take the newness off'.

There is an instrument called a Scangauge that I understand has the ability to send a stream of observations to a laptop. I have something similar for my older NHW11 Prius. This might be an approach for instrumenting your car and keeping a record of what happened. I'm planning to take one of my older laptops and making it into a permanent data recorder but that is something for another thread, another day.

I'll continue to poll this thread from time to time. However, it is perfectly OK to send a "PM" or "email" about any new posting to the thread after a couple of days or weeks. Please try to share the technical details with the community in this thread, there are some pretty clever folks here and I'm a strong believer in team efforts.

Can you tell me about the weather when these incidents have happened? In particular, was there a pattern of unusual dryness that might support a static electricity discharge through the accelerator assembly?

If anyone has an photos or detailed sketch of the accelerator assembly, I would be very interested. I've got some experience with the NHW11 version and I'm interested in the mechanical area that is blocked from ordinary view.

Unless the problem is diagnosed and corrected, I'm sure it will come back. All we can do is be a useful sounding board and offer our best expertise.

Bob Wilson

 

I came across that article a few days ago, while googling info on the '10 prius.
It scared me.

 

Any typo in the red-highlighted region above? do you mean the brake pedal?