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Unintended Acceleration - Find the Cause



  • emilspatsemilspats Member Posts: 1
    Has anyone considered the cruise control as the problem..maybe the chip?
  • dcalamiadcalamia Member Posts: 1
    edited March 2010
    Once I had a 1983 ford escort It did the same exact thing.I was going down the street and all of a sudden it accelertated to about 80mph. I didn't know wat to do. well when I finally got it turn off. I would turn the key off at a red light and turn it back on and take off . Well I finally got home safe and prayer, I checked my car out and found that the AIR FILTER HAD SUCK IN AND GOT CAUGHT UP IN THE FUEL INJECTORS, I took my car to a friend on mine and we clean the injectors. I told the ford dealer wat happen and they told me that they never heard of it. I should hope they check the air filters because sometimes they will go to pieces and will get suck in the injectors
  • humblepchumblepc Member Posts: 1
    First the cause may be plural rather than singular. Second, acceleration is under electronic control. By this I mean that software running on 1 or more microprocessors is making the final decision (incorrectly). What Toyota should be looking for is in the area of decision making by software/hardware . . . What are ALL the conditions that are possible across ALL the sensor inputs. Which ones have not been specified? What is the priority for handling sensory input? What is the sample rate for sensor input? What are all the latencies involved relative to decision making? Is there a supervisory level of decision making? Microprocessors are notoriously slow in making decisions and blindly doing whatever the software engineer has intended or mis-intended. When multiple microprocessors are involved the problem compounds nearly exponentially. If just 1 microprocessor goes off in the weeds all bets are off. The architecture of the electronic control obviously is flawed -- a software unified microprocessor controlled car will never be reliable period end of story. Is there an alternative? Yes. Consider an all in one HUMBLE (Hardware Unified Multiple Branch Logic Engine) decision making approach. See ecs-pc.com for a PC example of what I am referring to . . .
    It is no surprise these kinds of problems occur across ALL the various manufacturers . . . If you start with an imperfect-unreliable-time-multiplexed-latency-prone-software microprocessor approach, you end with an imperfect-unreliable-time-multiplexed-latency-prone-software microprocessor approach . . . The problems will persist . . .
    Good Will toward Toyota and ALL the other car makers -
  • djefxdjefx Member Posts: 1
    edited March 2010
    I am by no means an engineer however as an IT person believe that the issue has to do with the computer boards placed in the vehicle. To me, it seems more like the obvious than many of the techie answers here.

    As a person who changes out computer motherboards all the time, I've seen many computers boards that have had capacitors fail. The problem is not specific nor limited to one computer manufacturer either. Most of the capacitors however are manufactured by the same company because on just about every board replaced, these caps appears to be produced by the same company. Depending on which capacitor blows and what position it is on a computer board, it cause various issues with a PC. So what would the difference be with a car computer board? In a PC, I've seen caps blow that cause fans to rev up and in other cases, reboot consistantly, power up with nothing displayed, or not come on at all. A board that doesn't have the proper power being regulated can cause many issues, and it would seem to me, makes no differences when it comes to controlling a vehicle. Given the variables of heat and moisture, mix it with dirt, salt, and dust crossed with electricity, there is no telling what could actually happen.

    I guess the only true way to figure this issue out is to put an actual car in the lab environment and start shorting out some caps and.or resistors to see what happens.
  • sdahlbergsdahlberg Member Posts: 1
    The un-intended acceleration problem sounds like a software data integrity corruption problem. These occur when timing variations and subtle variations in the feedback control loops cause read/write corruptions. They are very subtle and are extremely difficult to detect, particularly for implementations across multiple processors and buses. This is likely a 10 x -12 to 10 x -15 probability problem.

    I'm an aerospace systems engineer and have a colleague who has a program that dynamically simulates simple models of the hardware/software interactions and automatically exposes the opportunities for software data integrity corruptions. This is the only automated method known to me to insure highly deterministic performance. It can be done manually, through brute force checks, but is only valid for that exact design implementation. Changing one line of code means it all must be done again from scratch.
  • djpwildmandjpwildman Member Posts: 1
    the cruise control is set accel by itself research this erea .comp or accel cruise valve :confuse:
  • ndowserndowser Member Posts: 5
    Wow you guys are putting WAY to much into this problem and it can be fixed EASY with *********. :)

    I was going to say but I think I'm going to read more about this 1 Mil there giving out and send the info to them.
  • lvisionlvision Member Posts: 6
    The total is $1,000,001 to find the cause of sudden acceleration in Toyota cars.
    Good luck to all including Toyota engineers.
  • evy88evy88 Member Posts: 1
    edited March 2010
    the cable that in the engine that is accelertion to the inside gas peddle could be split, causeing it to get stuck ,
  • jeffl4jeffl4 Member Posts: 1
    The only way this problem is going to be thoroughly analyzed and solved is if Toyota releases ALL the engineering data (circuit schematics, BOMs, source code, requirements documentation like UML etc.) for the ECU and all related modules to Edmunds "contestants" which they won't because they'll call it "proprietary" but really because it would be a gold mine to the hordes of attorneys seeking to file claims against the corporation. The REAL problem is that regulators like NHTSA and the FDA don't understand how to precisely control software development (and especially because they aren't funded to do so) like the FAA does. I've been involved in certifying software development to the most safety-critical levels (A and B) of RTCA DO-178B (the primary software safety development document used by the FAA) for over a decade, and from what I can tell the documentation (and ESPECIALLY testing!) required to submit a project for NHTSA approval is a sick joke by comparison. (Start with the fact that a safety-aware throttle would need TWO accelerator potentiometers so no single failure in HARDWARE OR SOFTWARE could cause the system to fail) Sure we could "speculate" that the code in the Toyota throttle-by-wire system fails to be deterministic, but is that due to running out of a resource like memory from excess fragmentation, is it "deadly embrace" or "priority inversion" of some task, is it perhaps from a "persistent interrupt" resulting from something like comm failure on the CANbus controller, or is it something "extraneous" such as excessive EMI? The only people who will have access to the documents that will show the design down to this level will be Toyota's engineering staff (who I'm sure by intent can't participate) and any people who know them who they could leak this information to, hence contest participation is by design unfair and this entire premise should be halted immediately. (I have to confess though that it would be fun to get a look at that information and see where the designers screwed the pooch!)
  • roadwarrior69roadwarrior69 Member Posts: 1
    edited March 2010
    ford had a similar problem in the early to mid 80's with the one way vacuum check valves in line with the cruise servo.the valve would leak causing the cruise servo to fully accelerate.
  • ndowserndowser Member Posts: 5
    Add a pressure sensor to the pedal and if the TPS says wide open throttle and the pressure sensor says no pressure than cut the acceleration and log the event in the computer and have the check engine light come on, also add some sensors in some key spots and log all the voltages of each at the time it happens so you will be able to find the problem.
  • tugmantugman Member Posts: 2
    Vehicles come over in ships called RO ROs for Roll on Roll off..they are completely sealed..
  • tugmantugman Member Posts: 2
    I am sure it has been already said but my take is that it is not the gas pedal but more likely the transmission. the sensors in the transmission thinks that the engine is not up to the appropriate RPM and increases the engine speed to compensate. The signals from the transmission are sent to the ECM ( electronic control module and when they get confused the one with the highest priority takes command..
    Thats just my take on it...That is why I only restore pre 1975 cars
  • okwhatnowokwhatnow Member Posts: 1
    edited March 2010
    My theory is simple. The microprocessor responsible for throttle control has a stack overflow due to an overwrite of system variables stored in memory with the call stack caused by sensor monitoring. This causes the microprocessor to return to the wrong address and then things go south. It is commonly assumed that the watch dog timer will catch this problem - the only difficulty is that it is possible that code not intended to execute does in fact execute that changes the watch dog timer interval - this keeps failsafe software from executing and you get what some are reporting - sudden acceleration without being able to turn off your engine using the ignition switch.

    A fix - if the problem can not be found - is to add a circuit that requires the throttle control to be undated in x amount of time - it it is not the gas is let off - so instead of crashing full speed into something you get rear ended by another vehicle and your auto explodes like the Pinto did.

    This defect would require a lot of previous state conditions to occur. Since it is rare - I would expect that this is in fact what it is. Bottom line it is a software problem that can not be detected through normal testing and design verification analysis will be the only way to catch it. But untimately it is simple. Not enough stack allocated or the stack not being protected or protected using faulty methodology.

    There is also the possibility that there are stack overwrite failsafes in the software so that when a stack overwrite is detected either too late or causes a state that can not be recovered from - since the watchdog timer fires - the stack overflow detect occurs again - and this just ends up in a unrecoverable loop.
  • cbrechlincbrechlin Member Posts: 11
    A properly designed fail-safe circuit could not allow factors such as cruise control to accidentally trigger. I'm not saying it is not being caused by cruise control, but that a genuine "Comparison Circuit" which self-monitors both the positive and negative actions of every involved switch and sensor every 5 ms to guarantee every condition is alive and within tolerance BEFORE permitting any acceleration is the only guarantee. I'll try to clarify why this type system would rectify the main one you describe.

    Say a stray signal out of the cruise control spikes the acceleration control. A double-parallel circuit is reporting that the cruise control button is in "Rest" position on both channels, then the Comparison circuit takes note of that every 5 ms. When the spike comes without a matching "On" position from both positive and negative reads of the cruise control button then the comparison circuit rejects the artificial spike as a false command. Stretch the idea in a different angle and say the cruise control button is sticky and does not sit 100% at rest or in the On position. The accelerator comparison has to be designed to monitor all components that affect acceleration including the cruise control obviously. The first time there is a 5 ms inconsistency in the function of the cruise control button the system is alerted because either A) "Rest" is Off while "On" is not On, or, B) "On" is On while "Rest" is not Off... this is how every device including the comparison circuit is designed to function.

    This type of self-monitoring circuit design won regulator's praise when it proved flawless. And I've mentioned in previous remarks that the main problem you get with these systems is the inability to operate because everything is NOT perfectly within tolerance, that slightly worn cruise control button brings an error code. Our system included a cache of every function of the comparison circuit for the prior 15 seconds before any fault. When you pull up the error readout you can view in sequence both channels of activity like a Flight Data Recorder, and then zero in on the trigger event, the worn cruise control button whose tolerance exceeded the 15ms threshold in its actuation for instance, that gave a single false-positive and disallowed acceleration and averted machine-based fatalities.

    All this is aside from mechanically sticky accelerator levers, but according to the Chicago Tribune this morning, eight people who were repaired mechanically for this problem have reported that they've already had unintended acceleration again, and they believe it's computer issues and NOT mechanical. You certainly can imagine people who've already been through this life threatening ordeal paying excruciating attention to the effects of this problem right?!

    IMO, Toyota and all other manufacturers must have such a fail-safe on electronic accelerator controls and that's going to mean replacing every out-of-tolerance switch in the world that fails the comparison circuit installations which will dictate acceptable engineered tolerances of all sensors and switches. They might be better off engineering a throttle-body mod and spring loaded cable as a genuine mechanical solution for older models and possibly less expensive.?. These systems simply must default off one way or another.
  • drivemecrzydrivemecrzy Member Posts: 1
    In reality this process of finding a (fix) for toyota's current recall problem is both comical and logical. break away from the engineers who are human, and did'nt foresee this problem.And look to all possible trouble shooting ideas. some consumers may frown, but how many times have we solved our own hiccups in life. I have driven toyotas in bussiness and personal for many years. Two of my trucks exceeded 300 thousand miles. back in 1989 one the work trucks had this problem, i designed my own gas pedal with an adjustable block on bottom of pedal, which allowed me to find point of failure. Yes i know the models today are based on electronic knowledge. so i would go back to the lab, find last model-year which did'nt have this issue. then compare electronic and physical design changes. i beleive there you find possible (design mistake) as my grandad said if it is'nt broke dont fix it. this may be the most cost effective path to solution. And yes, the least amount of cost here will prevent me from purchasing my toyota next year.If i had a degree i'd be at toyota,because i've always beleived they built their automobiles with our safety as first concern. thank you m.stinger
  • wolfman66wolfman66 Member Posts: 1
    The cause of the Toyota sudden acceleration is caused from the accelerator pedal being to close to the brake pedal. When the driver goes to press on the brake pedal, rarely they can be pressing on the gas pedal at the same time. When this happens the gas will override the brake causing the driver to press more on the brake giving more gas to the auto. This is more likely to happen when wearing large boots (work or winter).
    This can be fixed by moving the accelerator pedal further away from the gas pedal.
  • wjvjr727wjvjr727 Member Posts: 1
    The Japanese couldn't code (firmware) in the 1970's and they still can't today. I graduated from RPI with a B.S.E.E. (1980) and a M.Eng.E.E. (1982), so I've seen it firsthand.
  • 4552045520 Member Posts: 3
    I think the cruise control problem make a unintended acceleration but not only set on cruise control WITH WEIGHT. When I got back from vacation my father and another 2 family member pick me up. We drove my corolla and I was driving the car. I set on the cruise control rpm shut up 7000. My family member WEIGHT average 150 pound and my luggage about 70 pound. Also I have a same experience with camry. Now I drive a 2008 highlander nothing happen yet.
  • cbrechlincbrechlin Member Posts: 11
    I agree, I think this is where the main issue resides.

    The Chicago Tribune this morning reports that seven (I falsely stated eight previously) of the users who already got mechanically 'fixed' for unintended acceleration have experienced this again:

    "7 Drivers allege recall did not fix acceleration problems"

    Having previously gone through this frightening experience you can assume these people were paying attention to the pedal, yet they believe it's computer caused!

    My arguments on this thread point to a fundamental problem with the fail-safe/comparison-circuit design as you articulate... I think there's no other way for unintended acceleration to occur, outside of a raw mechanical failure like a stuck down-pedal or stuck throttle valve, a faulty fail-safe is imbedded.
  • drzmandrzman Member Posts: 1
    I agree with the general approach. I was leaning more toward a simple rollover error. Since this is a simple A/D type control system if there was a roll over from FF to 00 the control system would possibly keep winding up to meet the target value which due to the overflow is now far away. all aspects of the system would work as normal.
    The fact that by sticking a mechanical limiting device in the peddel appears to help may keep the signal below the FF threshold.
    Could be a simple "home sense" issue.
  • ounceofpreventounceofprevent Member Posts: 1
    I have experienced similar problems before with electronics components which support the aerospace industry. However, we do a much better job with taking responsibility and fixing problems immediately. As a result, on my watch no one was injured and we saved lives! We contacted all the customers with the equipment and--while not tackling the root issue right away--offered band-aid solutions to prevent their reoccurrence. This is shameful, not only to Toyota, but to the entire engineering community. Engineers must stand up and demand to be heard more.

    Enough preaching, I guess. Keep reading though....

    As microchips get smaller and smaller and the electromagnetic spectrum all around us gets busier and busier, the electronics components, in fact, behave as though they are tiny antennas. Commands get interrupted and software gets corrupted. Hardening is the Answer. Simply cover the chips with very thin gold leaf. The cost per unit part may be less than $25 (of course, the labor will be more).

    It is narcissistic to think we can possibly know everything that is going on all the time with these sophisticated components. This is another "Titanic type" case study in which we do not understand the performance of materials in their fielded environment Technology has gotten ahead of the root science here. It may take decades before we fully comprehend what has been going on. We must be willing to know that we do not know everything right now.

    Innovative uses of intelligent databases will prevent all future problems like this and, most importantly, save lives. I can show anyone who is interested how to do this. The technology is ten years old. The only thing that is needed is the will to do it. You do not need to understand all of the science now, just be willing to share and communicate experiences directly between engineers and customers through modified CRM programs.

    The automotive industry can learn a lot about the dedication to quality found in the aerospace industry.

    I look forward to the discussion.
  • cbrechlincbrechlin Member Posts: 11
    Excellent post jeffl4, both the competition and the Toyota software are fundamentally defective.
  • ndowserndowser Member Posts: 5
    Like I said you guys are making the problem harder than it is, it does not matter if the problem is the transmission or cruse control or anything else, program the ECM that when there is no pressure on the gas pedal and the brake pedal is applied deny all request from all devices (other than idle control to prevent the engine from stalling out) to increase the acceleration.
  • gcoburngcoburn Member Posts: 1
    One possible cause of the Toyota Sudden Acceleration Issue that I have heard is the possibility of electromagnetic interference that could cause a sudden problem with the electronics. I was riding down the freeway in southern California the other day and I noticed once again the sensors in the road that are used to measure traffic on the road. These sensors are also installed at just about every intersection where there is a traffic signal. These sensors, you've seen them, are about 2 feet in diameter and they are embedded in the pavement. You can see the circle cut and refilled with tar where they are installed. Some people think these are weight based sensors but they are not. They are nothing but large electro magnets that emit electromagnetic waves. When a large chunk of metal, ie: a car gets near them the magnetic field changes and is detected. I wonder if these are interfering with the operation of the electronics. Just a thought.
  • rm644rm644 Member Posts: 2
    An interesting read that discounts the theory of electromagnetic interference in Toyota vehicles...

  • jiml8jiml8 Member Posts: 9
    It was a 100 MHz Tektronix scope. Like I said, I wasn't collecting data, and didn't look much beyond spotting those spikes. Changed the alternator, problem solved. I returned the old alternator for the core charge. Wish now I'd kept it.

    After all, the alternator still charged the battery. This makes it "good" by most historical criteria. However, since it now provides power to sophisticated electronics, the requirements on its output are much more demanding.
  • jiml8jiml8 Member Posts: 9
    I do not disagree with the idea you put forth, and given the critical nature of the application, more redundancy/safety is better. However, if what I suggest does turn out to be the problem then what you suggest won't help.

    If voltage spikes on the power line make it all the way into the silicon, random switching will occur, in which case the software can't be trusted; literally anything can happen. Anything that depends on the software - such as a monitor to determine the state of a switch - may or may not work at all, and may or may not have accurate historical data. This is the essence of "illegal state". This is why, under any circumstances, a hardware device should be available to force a reset of the computer if it fails to respond appropriately in a specified timeframe. The forcing should be hardware, not software or firmware. Cycling power would be the safest way to do it., I think.
  • jiml8jiml8 Member Posts: 9
    Probably most claims about unintended acceleration were operator error, where the driver won't admit it or panicked and doesn't realize it.

    In older cars, there was no credible mechanism for unintended acceleration.

    Today, such a credible mechanism does exist; there is no mechanical connection between the accelerator and the throttle.

    Also, last Sep, there was a 911 call where a passenger very calmly told the operator what the driver was doing to try to make the Lexus stop. The call ended when the Lexus, driven by an off-duty cop, crashed at high speed.

    There certainly does appear to be a problem. While it is Toyota on the hot seat right now, it seems unlikely to be strictly a Toyota problem. As someone else mentioned here, the automotive industry does not have to go through the certification procedures that the aircraft industry has to go through, and if we are going to do "drive by wire", the auto industry SHOULD have to pass similar certifications.
  • wwestwwest Member Posts: 10,706
    You might have been looking at a failed "damper, damping resistor across the rotor elctromagnetic coil. Modern day alternator/regulator systems, regulator typically integrated into the alternator case, rely on a PWM technique for regulating the alternator output.

    Full battery voltage is applied to the rotor coil until the alternator output rises to a predetermined value, let's say 14.3 volts, for instance. Once the alternator output rises to that value the battery voltage to the rotor coil is switched off(***). Due to the now decaying magnetic field in the rotor the alternator output begins to fall. Once the alternator output voltage has fallen to ~12.5 volts the full battery voltage is again applied to the rotor coil.

    The above sequence is repeated at a frequency dependent on the overall time constant of the battery/alternator circuit, typically a Khz or more.

    *** This is the important point. If the battery source voltage were simply switched off, like happens with the A/C electromagnetic clutch coil, the rotor voltage would almost instantly rise to the point of arcing across the battery voltage switching device, old style mechanical relay or today's solid state "switch".

    But within the alternator's voltage regulator, in parallel with the rotor coil, is a fairly high wattage resistor. This resistor acts as a voltage "damper", soaking up, damping, the surge voltage that the rotor coil would otherwise generate.

    Should that damping resistor fail the result would be a much more rapid PWM rate along with HUGE voltage spiking on the 12 volt battery circuit.
  • overspooledoverspooled Member Posts: 2
    There have been many different accounts of the actual problem, many of which don't seem mechanically feasible. The inter connections electronically between the fly by wire systems, cruise control and the pedal assembly are all suspect.
    The frequency of the problem makes analysis difficult. Mechanical failures are usually not as intermittent. Electronic failures, or anomalies require a trigger, something to aggravate the symptom. Insufficient wiring/ shielding/ grounding is an area that would be suspect. As space becomes tighter, more and more connections are packed into tighter spaces. Some of these lines can create magnetic or frequency interference depending on routing. I think some detailed investigation of the engine control/ body harnesses might be well spent. A failure in the pedal assembly could cause an acceleration signal to be continuously triggered, but it does not explain some of the other accounts. There is always a possibility of a problem with multiple causes...
  • jiml8jiml8 Member Posts: 9
    That sounds credible, and could certainly explain everything.
  • wwestwwest Member Posts: 10,706
    Since CC began to be used back in the lack 60's there has always been a failsafe system incorporated. The CC constantly monitors the brake light circuit and is instantly disabled if the brakes are applied. The brake detection circuit even has a low voltage "keep-alive" resistor such that if the brake light circuit is open CC will not engage. Frustrating times for a driver with all the brake light bulbs failed or removed, or having substituded LED bulbs.

    Should the brake light switch fail there is always the backup CC "off" switch.

    The Toyota/Denso DBW system already includes dual sensors, both at the gas pedal and at the throttle plate. According to the documentation the ECU, microprocessor, is supposed to be constantly monitoring both sets of sensors. This "monitor" software constantly checks that the two sensors are tracking each other correctly, with the correct range, and the voltages are of separate enough values to discern they are not shorted together.

    As Dr. Gilbert demonstrated, the Toyota/Denso "shorted together" monitoring voltage "window" is out of tolerance with reality. The nominal separation voltage is 0.80 volts and in order to detect a short the signals must be within 0.02 volts. 0.40 volts would have been more appropriate IMMHO.
  • 77coupdeville77coupdeville Member Posts: 1
    This may have been mentioned and checked by Toyota, but a simple possibility is a weak accelerator return spring, a binding throttle plate, binding accelerator pedal linkage, a binding/kinked cable, or any combination of the above. Remember Occam's Razor, which states that the simplest explanation is usually the best.
  • geicageica Member Posts: 1
    Kinda too early to fully disclose thoughts.Its that the issues are not always present day. The history of past and present lead up to current trends. Thats all I will say for now. PO box 7420 jacksonville , North Carolina 28540
  • vindogg08vindogg08 Member Posts: 1
    Do you know what that would do if they would have to pass similar certifications????? WOW! Do you know how much airplanes and airplane parts cost? Obviously not!!! Airplanes and airplane parts cost so much because of all the rules and certifications. Yes some need to be there, but that means a car would have to be tested for hours before if could be used, inspected head to toe which would increase the cost to build a car, which would then get passed on to the consumer! If the car or brand doesn't work, don't buy it or buy something else! Don't let the government control the situation. All it will do is increase the price of cars dramatically, to as much as buying an airplane!!! Get educated before you post something!
  • wwestwwest Member Posts: 10,706
    My best guess is that some external event, RFI/EMI event, or even a voltage spike, surge, drop on the 12 volt supply system, is resulting in an out of order instruction sequence execution.

    The out of order execution results in "setting" a variable(X) within the firmware code that indicates that the CC is in the "Set/Accel" position. With that variable(X) "set" "true" the car would begin to accelerate indefinitely.

    Step on the brakes and the appropriate firmware executes which would normally disable CC but doesn't reach that execution point since it first checks another variable(Y) that indicates CC is not engaged. There is more than one possibility for "Y", CC active, not being set "true". First, the aforementioned external event, or there is the possibility of a code fault, oversight, and the "Y" variable will not be set until the "set/accel" button/function is released. Obviously this latter event is now just NOT going to happen.

    Suppose a person happens to "tap" the brakes, left foot braker, just at the very same instant (at the nanosecond level) CC set/accel is depressed. The "brake-on" firmware routine executes first but there is no "X" variable to clear/reset. Immediately thereafter the CC set/accel routine executes.

    And now suppose the driver NEVER again releases and re-applies braking.
  • wwestwwest Member Posts: 10,706
    Do you know how much airplane "part" certification would cost on a per unit basis if ~2,000,000 of them were sold each year...??
  • wozmachinewozmachine Member Posts: 1
    It appears to me (from youtube videos and ttac.com diagrams) that the compression spring pack (a spring within a spring) on the CTS provided gas pedal does not fully guide or anchor the springs to the housing. The "shim" fix does this. The Denso pedal design anchors and constrains the springs. The orignal patent held by CTS shows torsion springs which are costly and take a greater amount of time to assemble. CTS claims they build the pedal per Toyota spec. Examination of the spring pack after a jam should confirm the binding of the springs in their compressed (full throttle) state.
  • a_l_hubcapsa_l_hubcaps Member Posts: 518
    "A properly designed fail-safe circuit could not allow factors such as cruise control to accidentally trigger."

    I understand what you're saying, but you're thinking about monitoring for faults in switches and sensors while assuming that the software is written correctly.

    What I'm imagining is something like this (purely theoretical since I have no idea how Toyota's software is actually structured): Suppose there's a code module that handles cruise control inputs, by monitoring and interpreting the state of the cruise switches. Then, separetely, suppose there's a code module that handles controlling the throttle position by sending commands to the throttle assembly. In this scenario, all the sanity checking for the cruise hardware (monitoring switch states and such) would be handled by the cruise code module.

    Now, suppose there is a shared space for data passing between these modules. Let's say there are two variables, call them cruise_state and cruise_speed. If the driver sets the vehicle to cruise at 65 MPH, the cruise code module would set cruise_state to 1 and cruise_speed to 65. The throttle code module would periodically check these variables to see whether it needs to move the throttle in response to a cruise command (or cancel) from the driver. Since the cruise inputs have already been sanity-checked by the cruise code, the throttle code trusts that the data in those two variables accurately represents the driver's inputs and does no further checking. Now suppose some other routine overruns a buffer and overwrites cruise_state and cruise_speed with all 1's. The throttle code does its next check of the cruise variables, finds nonzero cruise_state and cruise_speed == 255, and we're off to the races.

    This is just a toy example; I'm sure there are a lot more complexities and differences in the real system. I haven't done this kind of embedded control programming so I don't know what the standard techniques are, but I've done enough low-level C stuff to know that all kinds of interesting things can happen that are hard to duplicate because they only happen under rare conditions.

    I guess this is one of those problems like the old "an engineer, a physicist and a programmer in a broken-down car" type jokes -- everybody's input is based on the field they're familiar with. The discussion about electronics and interference has been interesting to me because I don't know much about it.

    -Andrew L
  • pav245pav245 Member Posts: 1
    I have worked in both the computer and automotive industry. The capacitors in the auto industry are much more robust ( and expensive) than the caps used in the PC industry, meeting Mil Specs that the computer industry never cared about. Printed circuits boards on automotive almost always have conformal coatings for protection from the elements.

    Most PCs won't work at even moderate extremes of temperature whereas automotive applications have an extremely large temperature range, especially in underhood applications. Comparing PCs to Automotive really isn't a fair comparison.
  • overspooledoverspooled Member Posts: 2
    While there is truth to what you say, not all components are insulated from the elements. Toyotas have in older moldels had issues with tachometers/ odometers as a result of cold solder joints and corrorsion...
  • controlengcontroleng Member Posts: 1
    I have been designing microprocessor based control systems, the hardware and software for 37 years starting with the intel 4004. The problem with the Toyotas is extremely simple. In the firmware for the computer
    there is a section of code that allows the throttle to be 'opened' more than the gas pedel sensor value says it should be. There are potientially many causes of this but they all cause the microprocessor to make an overriding decision to send a higher value than the 'throttle request' value would indicate. The real problem here is lack of experienced and failsafe programming methods. This is a boundry value problem and a value that the designers never applied to the software. It occurs infrequently enough that a novice control engineer, i.e. virtually every far east 'programmer' would miss. The code needs to written and any code that causes the throttle control value to mathmatically exceed the throttle request must be removed. It is probably in the IDLE subroutines or in the actual throttle position sensor if they were stupid enough to make that a feedback loop. I encountered this problem before when making a marine engine electonicly controlled. They probably use a carbon film resistor for the sensors. Real bad idea. I use wire wound sensors, no spikes or opens. I am going to the junk yard tommorow to frankenstein a brain, gas pedal and throttle body.

    By the by, an alternator spike or em would not effect capasitor secured power to a microprocessor. If that were the case the micros would have gone haywire before they even left the assembly line. Get real people. Get an emulator and a logic analyzer.
  • wwestwwest Member Posts: 10,706
    "..an alternator spike or em would not cause.."

    Even if the RFI/EMI "spike" entered the control module via an input or output signal or ground wire..?? And what about common mode grounding problems..?? The "ground" voltage at the sensor or servomotor being significantly different, due to a 100 AMP surge current to the 12 volt ABS pumpmotor...?

    Until you can reliably replicate the failure an emulator and/or logic analyzer will be of no help.

    Intel 4004....You must be about my age, the first I4004 I bought was in ~1972.
  • wwestwwest Member Posts: 10,706
    In CC the gas pedal can be at the idle position when the throttle plate is wide open.
  • atlgaxtatlgaxt Member Posts: 501
    No car will override its brakes. Every gear shift has a neutral slot. Are we to believe that Toyotas are suffering multiple failures that leave no trace evidence?

    What we are seeing is driver error and mass hysteria. Of course the media is piling on, just like they did to Audi 20+ years ago.

    And really folks, now that the government and the unions own GM is it suprising to see Toyota executives being beat up in front of Congress? It's called Chicago style politics.
  • indymavindymav Member Posts: 1
    I think there is too much electronics involved. The more electronics the more the problems. Go back to a cable to throttle concept and make it simple.
  • goldsuvgoldsuv Member Posts: 51
    This is what the NHTSA said about full throttle braking distance when they tested a 2007 Lexus ES350

    "Testing conducted by VRTC determined that the brake pedal force required to stop a subject vehicle with a wide open throttle was significantly greater than when the vehicle is operating with a closed throttle.
    Significant brake pedal force in excess of 150 pounds was required to stop the
    vehicle, compared to 30 pounds required when the vehicle is operating normally.
    Stopping distances increased from less than 200 feet to more than 1,000 feet."

    This is from a NHTSA report that can be found at
    They also tested for EMI and found no problems.
    "The Vehicle Research and Test Center obtained a Lexus ES350 for testing. The
    vehicle was fully instrumented to monitor and acquire data relating to yaw rate,
    speed, acceleration, deceleration, brake pedal effort, brake line hydraulic
    pressure, brake pad temperature, engine vacuum, brake booster vacuum, throttle
    plate position, and accelerator pedal position. Multiple electrical signals were
    introduced into the electrical system to test the robustness of the electronics
    against single point failures due to electrical interference. The system proved to
    have multiple redundancies and showed no vulnerabilities to electrical signal
    activities. Magnetic fields were introduced in proximity to the throttle body and
    accelerator pedal potentiometers and did result in an increase in engine
    revolutions per minute (RPM) of up to approximately 1,000 RPM, similar to a
    cold-idle engine RPM level. Mechanical interferences at the throttle body caused
    the engine to shut down
  • jiml8jiml8 Member Posts: 9
    Yes I do know what all that costs; I did design and development work in aerospace for many years.

    But if we intend to drive by wire, we have to bear the cost. There should be a zero percent probability of a car running away with the passengers and being unstoppable.

    If that goal is to be achieved, then we need the reviews and certifications.

    If that goal is not to be achieved, we shouldn't be doing drive by wire. It is easy enough to say that "the genuine incidents of a car running away are so rare that it doesn't matter", but if it happens to you or your family you might think otherwise.
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