Auto Repair Library, Auto Parts, Accessories, Tools, Manuals & Books, Car BLOG, Links

Toyota unintended acceleration

What Caused Toyota Unintended Acceleration?

By Larry Carley Copyright 2009-11-12

Recent news reports of Toyota sudden unintended acceleration being caused by mispositioned floor mats will probably turn out to be bunk. I suspect the real cause will turn out to be an electronic glitch in the throttle-by-wire system.

Like many other vehicle manufacturers, Toyota dropped the old fashioned throttle cable that used to link the gas pedal to the engine throttle. In its place is a computer-controlled throttle-by-wire system that uses an accelerator pedal position sensor. When the driver steps down on the pedal, the request to "go faster" is sent to the computer. The computer then commands a small electric motor on the throttle to open the throttle wider. A throttle position sensor on the throttle monitors the throttle opening, and the corresponding increase in engine speed is noted by the computer.

Is throttle-by-wire failsafe?

Throttle-by-wire is supposed to be failsafe, but apparently it is not. The accelerator pedal sensor actually contains two sensors, not one. If both sensors do not report the same amount of pedal movement to the computer, it is supposed to set a fault code and go into a default mode that limits the throtle opening. Likewise, if the engine throttle fails to open or close as commanded, that should also set a fault code and put the system into a default mode.

But strange things can happen in electrical circuits as well as the control electronics. In the case of the Toyota sudden unintended acceleration problem, something is apparently happening in the control circuit that is commanding full throttle even though the driver may not be touching the gas pedal at all.

I can only speculate as to what might be causing this problem. But I suspect that it will turn out to be an electronic fault in the accelerator pedal sensor circuit wiring harness that is giving a false "full throttle" command to the computer. Or, something could be shorting battery voltage to the throttle control motor causing it to go full open. Or, there is an electronic glitch or programming fault in the cruise control system that is commanding full throttle while driving.

Cruise Control Involved?

Since most of the reported instances of sudden unintended acceleration have occurred while highway driving, I would suspect a link between the cruise control system and the throttle control system.

What happens if the cruise control system loses input from the vehicle speed sensor? Does it shut down or does it try to increase speed by opening the throttle all the way? I don't know.

When you step on the brakes while driving in cruise control mode, most cruise control systems disengage until you press the RESUME button. The drivers who have experienced sudden unintended acceleration say standing on the brakes has had little or no effect in slowing the vehicle or returning the engine to normal speed. The throttle stays wide open and the vehicle continues to accelerate. Again, this might imply some kind of fault in the cruise control system logic, or possibly in the brake pedal switch circuit that tells the system when the driver is depressing the brake pedal.

Is it a Control Logic Fault?

Because the sudden unintended acceleration problem has been reported in a number of different Toyota and Lexus models, the cause my turn out to be the programming of the throttle-by-wire control system. One difference between Toyota/Lexus and most other makes is that Toyota does NOT have a back-to-idle failsafe mode if the control system detects a conflict between the brake and accelerator pedals. In other vehicles, if the driver is pressing down hard on both pedals at the same time (like old fashioned power braking), or the computer receives inputs from the brake pedal switch and accelerator pedal position switch that both are being pressed simultaneously, it commands the engine throttle to close to the idle position. This allows the vehicle to stop in a shorter distance, and also averts the possibility of a runaway car if something is amiss. Why this is not part of the Toyota/Lexus control logic, I don't know.

In any event, if floor mats jamming the gas pedal is not causing the problem (which many of those who have experienced sudden unintended acceleration claim is NOT the cause), hopefully a close review of the wiring schematics and control logic will reveal a design flaw or programming glitch that is causing the runaway cars.

What To Do If Your Toyota Prius Accelerates Unintentionally

1. Keep a cool head and remain calm. But reacting quickly to the situation is absolutely essential to minimize your risk of an accident.

2. If the engine is accelerating uncontrollably, hit the brakes as hard as you can and maintain firm and steady pressure on the pedal. Your vehicle should slow down.

3. If the engine fails to respond, or the brakes are not having much effect, switch the ignition key to the ACCESSORY position (not all the way off as this may cause the steering column to lock!). If your vehicle has a STOP/START push button, push and hold the button in until the engine quits. On Toyota and Lexus, this can take up to three seconds, which may seem like an eternity if your vehicle is speeding out of control down the highway.

4. If you can't shut the engine off, shift the transmission into neutral (if you have an automatic) or depress the clutch pedal (if you have a stick shift). This will disengage the engine from the drivetrain and allow the brakes to slow the vehicle. However, the engine will continue to race so try to shut it off as quickly as possible to prevent possible engine damage.

5. Once you have the situation under control (engine off, car slowed or coasting to a stop), pull over, stop the car, get out and call a tow truck. Have the vehicle towed to a Toyota/Lexus dealer or a repair shop for diagnosis. Your vehicle may be unsafe to drive. I would not drive it again until a technician has had an opportunity to check the computer system for fault codes or other glitches.

6. If you have had a scary experience with sudden unintended acceleration, but the new car dealership or other technician was unable to find anything wrong, I would be very leery about driving the vehicle home. The same thing could happen again. That leaves you in a real bind. Should you take your chances and drive a car that may suddenly speed up, or should you demand the dealership keep it until they can guarantee they have fixed it, or should you dump the car then and there and buy another car? None of these are very good options. Hopefully, Toyota can get this figured out.

Update: January 28, 2010

Toyota Issues Massive Recall to Fix Unintended Acceleration Problem

Toyota has issued a recall on about 3.4 million vehicles in recent days to fix a "sticky gas pedal." The recall includes 2009-2010 RAV4, the 2009-2010 Corolla, the 2009-2010 Matrix, the 2005-2010 Avalon, the 2007-2010 Camry, the 2010 Highlander, the 2007-2010 Tundra and the 2008-2010 Sequoia. Toyota has also asked its dealers to temporarily suspend the sales of these vehicles until the problem can be fixed.

Toyota says that its supplier, CTS Corp. of Elkhart, Indiana, is producing replacement gas pedals for the affected vehicles, and that the parts are being shipped to Toyota so its dealers can replace the original units on the vehicles in the recall.

Toyota says the problem appears to be due to corrosion forming inside the accelerator pedal unit that prevents the gas pedal from returning after it has been depressed. Apparently, the springs inside the unit are too weak to overcome the resistance created at the hinge point by corrosion. Toyota says the corrosion is due to moisture seeping into the accelerator pedal unit.

This probably isn't the final chapter on this issue as I suspect there may be more to the problem than corrosion causing a sticky gas pedal. It may require reflashing the PCMs to add a brake override safety command to disengage the throttle when the brakes are applied. That will require adding or changing a few lines of code in the PCM software, which in turn will require dealers to reflash the PCM with the updated calibrations (a process that typically takes about 45 minutes per vehicle using a factory scan tool).

Update: February 26, 2010

Toyota Unintended Acceleration Problem Linked to Inability to Detect Throttle Control System Faults

Toyota's unintended acceleration problem is blamed on an electronic fault, not a sticky gas pedal or pedal jamming due to misplaced floor mats. According to David Gilbert, a professor of Automotive Technology at Southern Illinois, Toyota's unintended acceleration problem may be due to the fact that the PCM self-diagnostics can't always detect faults in the engine's electronic throttle control system or accelerator pedal. This can prevent the car from going into a fail-safe mode if a fault occurs in the accelerator pedal sensor or throttle control system.

News Update: March 9, 2010

Runaway Prius hits 94 MPH Before Driver is Rescued by Police

runaway prius video

This CNN news report
tells about a runaway Toyota Prius in California hitting speeds of 90 mph before the driver was rescued by police after calling 911 on his cell phone. A patrol car caught up with the speeding Prius and was able to help the driver slow his vehicle. The driver was standing on the brake pedal with no effect because the brakes were too hot and had faded. After being told to apply the parking brake, the vehicle was finally able to slow down, and eventually the driver was able to shut the engine off. Scary stuff!

News Update: March 89, 2010

SRS Reports 3306 Incidents of Toyota Unintended Acceleration, and 39 Deaths!

According to data compiled by Safety Research & Strategies (SRS) investigation into the Toyota unintended acceleration issue, there have been 3306 such documented incidents reported to the NHTSA and various media outlets to date, which have been blamed for 1159 accidents, 469 injuries and 30 deaths. During the Congressional hearings, Toyota admitted their own internal documents listed 37,900 customer reports that may be related to unintended acceleration!

News Update: July 14, 2010

Government Undecided as to Cause of Toyota Unintended Acceleration Problem

According to an Associated Press report released today, the NHTSA has not yet come to any conclusions about the cause or who is at fault in the Toyota unintended acceleration investigation. NHTSA says its engineers are continuing to investigate the possible causes of sudden acceleration in Toyotas, along with scientists and researchers with the National Academy of Scientists and NASA.

The Wall Street Journal, citing anonymous sources, reported Tuesday that the government had analyzed dozens of event data recorders, or black boxes, in Toyota vehicles involved in crashes blamed on unintended acceleration and found the throttles were open and the brakes were not engaged. That would suggest the drivers were stepping on the gas pedal instead of the brakes (or possibly that the electronic throttle control was running the engine at full throttle).

Transportation Department spokeswoman Olivia Alair said government investigators had "drawn no conclusions and released no data. She said the government would follow the facts and inform the public when the investigation comes to an end. Daniel Smith, NHTSA's associate administrator for enforcement, told a panel with the National Academy of Sciences reviewing unintended acceleration last month that the agency had not yet found any defects beyond the problems of pedals becoming stuck in floor mats and sticking accelerator pedals. The unintended acceleration in Toyotas may have been involved in the deaths of 93 people over the past decade. The agency has received over 3,000 complaints of sudden acceleration in Toyotas.

Toyota said its own investigation had found a number of explanations for the sudden acceleration, including pedal entrapment by floor mats, sticking gas pedals and the misapplication of the pedal - but no cases in which the electronic throttle control was the cause.

The NHSTA investigation is continuing, and is expected to be completed in the fall. The National Academy of Sciences is conducting a broader review of unintended acceleration in vehicles across the entire auto industry. The panel is expected to report its findings in the fall of 2011.

Toyota paid a record $16.4 million fine for its slow response to an accelerator pedal recall and is facing hundreds of state and federal lawsuits. Congress is considering an upgrade to auto safety laws in the aftermath of the Toyota recalls.

News Update: August 12, 2010:

Toyota Says No Electronic Faults Found in Unintended Acceleration Investigation

Yesterday, representatives from the National Highway Traffic Safety Administration (NHTSA) told members of Congress that preliminary investigations have not identified any new safety defects in Toyota products, other than sticking gas pedals or pedal entrapment. Below is Toyota's official statement on the matter:

"Toyota's own vehicle evaluations have confirmed that the remedies it developed for sticking accelerator pedal and potential accelerator pedal entrapment by an unsecured or incompatible floor mat are effective. We have also confirmed several different causes for unintended acceleration reports, including pedal entrapment by floor mats, pedal misapplication and vehicle functions where a slight increase in engine speed is normal, such as engine idle up from a cold start or air conditioning loads."

"Having conducted more than 4,000 on-site vehicle inspections, in no case have we found electronic throttle controls to be a cause of unintended acceleration. Toyota is committed to listening more attentively to our customers and continuing to investigate unintended acceleration concerns."

News Update: February 9, 2011

Government Report Says No Electrical Cause of Toyota Unintended Acceleration

The U.S. Department of Transportation (DOT) has released the results of its 10-month investigation of potential electronic causes of Toyota's unintended acceleration problem. The report says government researchers were unable to find any electronic faults that could have caused a runaway vehicle or unintended acceleration in Toyota vehicles. The only defects found were the two mechanical safety flaws that National Highway Traffic Safety Administration (NHTSA) had previously identified: sticking accelerator pedals and pedals that could hang up on floor mats. The report says these remain the ONLY known causes for the unintended acceleration incidents.

In 2009 and 2010, Toyota recalled nearly 8 million vehicles as part of the sticky pedal and pedal entrapment recalls. The automaker also paid $48.8 million in civil penalties as the result of NHTSA investigations into the timeliness of several safety recalls last year.

The 10-month NHTSA study enlisted NASA engineers with expertise in areas such as computer controlled electronic systems, electromagnetic interference and software integrity to conduct new research into whether electronic systems or electromagnetic interference played a role in causing unintended acceleration. No such faults could be found.

NASA engineers evaluated the electronic circuitry in Toyota vehicles and analyzed more than 280,000 lines of software code for any potential flaws that could cause the throttle to open wide. They also examined and tested the throttle control components to see if anything could cause an unwanted throttle opening. At a special facility in Michigan, NHTSA and NASA engineers also exposed Toyota vehicles to strong electromagnetic radiation to see if that might cause a malfunctions resulting in unintended acceleration. No problems were found.

In response to the NHTSA report, Steve St. Angelo, Toyota's chief quality officer for North America, said, "Toyota welcomes the findings of NASA and NHTSA regarding our Electronic Throttle Control System with intelligence (ETCS-i) and we appreciate the thoroughness of their review. We believe this rigorous scientific analysis by some of America's foremost engineers should further reinforce confidence in the safety of Toyota and Lexus vehicles. We hope this important study will help put to rest unsupported speculation about Toyota's ETCS-i, which is well-designed and well-tested to ensure that a real world, un-commanded acceleration of the vehicle cannot occur."

January 11, 2012

NASA Report Says Tin Whiskers May Be Cause of Accelerator Sensor Problem

A 30-page NASA report says the growth of microscopic "tin whiskers" across the accelerator pedal sensor contacts may be causing a short circuit that could make a vehicle accelerate without any driver input. Click Here to read the full NASA report.

March 2014

Toyota Pays $1.2 Billion Over Unintended Acceleration Issue

Toyota paid a $1.2 billion settlement to the U.S. government to avoid prosecution for covering up severe safety problems with their unintended acceleration problem. The deferred prosecution agreement required Toyota to admit it had misled U.S. consumers by concealing and making deceptive statements about two safety related issues affecting its vehicles, each of which caused a type of unintended acceleration.

Toyota said it investigated the problem and conducted a massive recall to address the problem of accelerators being stuck under floor mats. Toyota told motorists that shortening the accelerator pedal and making sure the floor mat did not contact the pedal fixed the problem. But Toyota later admitted that the recalls did not cover all of the cars that may have been affected. Toyota had also concealed another cause of sudden acceleration they had found during their investigations, which was sticky gas pedals. When depressed, the pedal would stick down and not return to the normal idle position.

toyota unintended acceleration Related articles:

Throttle-by-Wire Electronic Throttle Control

Controller Area Network (CAN) Diagnostics

Auto Accidents: Mechanical Problems That Increase Your Risk

Mitchell 1 DIY eautorepair manuals

Mitchell Repair Information for the Do-it-Yourselfer

Be sure to visit our other websites:
topyota unintended acceleration

AA1Car Automotive Diagnostic & Repair Help

Auto Repair Yourself

Carley Automotive Software