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Toyota's Engineering Process and the General Public
Doofus writes "The Washington Post has published in today's paper an article titled 'Why it's so hard for Toyota to find out what's wrong' by Frank Ahrens on the Toyota situation and the difficulties of adequately conveying to Senators and Representatives — most of whom are non-technical — the debugging process. Ahrens interviews Giorgio Rizzoni, an 'expert in failure analysis' at Ohio State, who describes the iterations of testing that NHTSA will likely inflict on the Toyota sample cars they have purchased, and then moves into the realm of software and systems verification: 'He explained that each vehicle contains "layers of computer code that may be added from one model year to next" that control nearly every system, from acceleration to braking to stability. Rizzoni said this software is rigorously tested, but he added: "It is well-known in our community that there is no scientific, firm way of actually completely verifying and validating software."' Ahrens ends the piece with a quote from a 2009 LA Times interview with former UCLA psychology professor Richard Schmidt about how user reports are often unreliable: 'When the driver says they have their foot on the brake, they are just plain wrong. The human motor system is not perfect, and it doesn't always do what it is told.'"
Toyota is currently planning an event to challenge evidence presented by professor David W. Gilbert that called into question Toyota's electronic throttle system.
come on, it's just a big conspiracy.
it's not like 100, 200, one thousand toyotas are
skidding of the highway and into a tree everyday.
there are like a handful of incidents.
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naw, this is just a big PR campaign of american motor
industry to smear superior japanese tech.
the prius is like a 5 year old car model and in all this
time american "muscle" motor never came up with an answer.
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big oil and big car a big happy american family.
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the engine (sic) that drives the (u.s.) capitalistic machine needs
consumption and waste, not innovation and thriftiness.
Less than 100 cars out of 8,000,000 have had this problem. That is a 0.001% failure rate.
Of those 0.001% of cars that had the problem, how many times did someone drive them before they failed?
I don't want to say this is user error, but I have seen some users do stupid stuff and not even know they did it.
Im a gamer, not a grammer major. This post is full of spelling and grammer mistakes.
btw - I hope your are right. I own a Prius, but not one with the problem, so I am unable to even try to help. If I did have one I would be disassembling the software system looking for potential overwrites of the variables that control the throttle calculation.
``Dismissing user reports is what got Toyota in trouble in the first place. Keep doing that. See how far it gets you.''
Right. Nobody I know about actually has a problem with there being a defect in the vehicles. The defect should not have been there and it's a great shame that it was, but everybody understands that it happens. If it happens too often, that gives you a poor reputation, but it doesn't happen to Toyota a lot so their reputation there is good.
Where Toyota went wrong is in how they handled the incident. What they should have done was err on the side of caution, notify people of a possible issue, and encourage them to be careful and report anything that might be related to Toyota to help them investigate the issue. Only after they would have done their best to confirm the issue could they have concluded that the issue does not actually seem to occur, and even in that case they should not have told people that there is no issue, especially not the people who report experiencing it.
What they did instead was deny that there was an issue before they had properly investigated it, and effectively called the reporters of the issue liars. Calling your customers liars is a very bad idea, and doing so with those who report a rarely occurring issue not only insults them, but also deprives you of an important source of information. It's probably the very worst thing they could have done.
Figuring out the parallel between this and full disclosure in computer security is left as an exercise to the reader.
Please correct me if I got my facts wrong.
The gilbert problem is the reading from the toyota ECM when the two redundant APP (accln pedal position) signal circuits are shorted together (main and sub), From the toyota camry VSRM :
DESCRIPTION
This ETCS (Electronic Throttle Control System) does not use a throttle cable. The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal bracket and has 2 sensor circuits: VPA (main) and VPA2 (sub). This sensor is a non-contact type, and uses Hall-effect elements, in order to yield accurate signals, even in extreme driving conditions, such as at high speeds as well as very low speeds. The voltage, which is applied to terminals VPA and VPA2 of the ECM, varies between 0 V and 5 V in proportion to the operating angle of the accelerator pedal (throttle valve). A signal from VPA indicates the actual accelerator pedal opening angle (throttle valve opening angle) and is used for engine control. A signal from VPA2 conveys the status of the VPA circuit and is used to check the APP sensor itself. The ECM monitors the actual accelerator pedal opening angle (throttle valve opening angle) through the signals from VPA and VPA2, and controls the throttle actuator according to these signals.
FAIL-SAFE
The accelerator pedal position sensor has two (main and sub) sensor circuits. If a malfunction occurs in either of the sensor circuits, the ECM detects the abnormal signal voltage difference between the two sensor circuits and switches to limp mode. In limp mode, the functioning circuit is used to calculate the accelerator pedal opening angle to allow the vehicle to continue driving. If both circuits malfunction, the ECM regards the opening angle of the accelerator pedal as being fully closed. In this case, the throttle valve remains closed as if the engine is idling.
If a pass condition is detected and then the ignition switch is turned off, the fail-safe operation stops and the system returns to a normal condition.
VPA and VPA2 are coming from the PCM with .5-1.1v at one of the sensors and 1.2-2.0v at the other when the pedal is at its relaxed position. When there's force at the pedal, one sensor will operate between 2.6-4.5v and the other at 3.4-5.0v.
Toyota specs normal voltage for both the VPA sensors between between .4-4.8v for VPA, and .5-4.8v for VPA2 with a .2v deviation between the 2 sensors. Anything out of those ranges will trigger a DTC
An internal short could occur within one or more of the paths from the circuits leading to the ecm. That could lead to a situation where the computer cannot detect its own failure.Therefore, when the system gets conflicting information, it arbitrarily ignores half the conflicting information. It does not know which of the circuits are lying or if they both are lying and shorted together. different resistance values will lead to arbitrary acceleration. Having the brake override it is a stopgap, but fixing the real problem (perhaps with a third circuit in voting mode which will require replacing the entire circuit path) or reversed sensors or log and opposing log sensors.
There might also be emi problems with induced magnetic fields in the CTS pedal assembly which detects induced emf as acceleration since it relies on induced emf to operate in the first place and is made of plastic. replacing with conventional denso rather than cts will also help.