Sudden Acceleration: Automakers' "Fail-Safe" Systems Guard Against Electronic Interference
This story came to me today from Tucson, Arizona: "My 2009 Toyota RAV-4 is currently in the shop getting Toyota's fix. Yesterday morning my wife was almost killed while stopping at a stop sign. All of a sudden, the car's engine started racing and only in the nick of time did she manage to stop it before being shot out into oncoming traffic--.My wife's foot was not even on the accelerator when the engine started revving. The floor mats were secured a good five inches away. Now they tell me it is fixed with a shim. I don't buy it and I am afraid to drive this car."
The key points here are that the driver's foot was nowhere near the accelerator pedal, and the floormats were not at issue. So what's going on here? It seems unlikely that either of Toyota's recalls will address what's going on with this RAV-4 (and many other cars that have experienced similar problems under similar circumstances). But finding an alternative cause is not a simple matter.
The idea that Toyotas (and other companies' cars, too) experience electronic interference affecting their modern throttle-by-wire systems is gaining steam. According to the Los Angeles Times, the first electronic throttles were introduced by BMW for its 7 Series in 1988, but the technology was soon adopted widely. The National Highway Traffic Safety Administration (NHTSA) is taking a "fresh look" at that issue, and no less a computer authority than Apple co-founder Steve Wozniak says it is software issues that is affecting his Toyota Prius. "Is my software bug also some code that is in the other Priuses and related to the deadly problem?" he asked.
It would be easy to jump to that conclusion, but today's cars offer redundant safety systems to guard against that happening. In throttle-by-wire, a sensor in the pedal sends a signal to a control unit, which analyzes it and then sends it on to the throttle. Carmakers love throttle by wire, because it enables sophisticated traction control and adaptive cruise (in which your car keeps pace with the one in front of it).
Toyota's throttle-by-wire systems were initially backed up with cables, but today there's a different form of redundancy. For instance, in the case of the recalled Toyota Camry, SAE International reports that the car actually has two accelerator position sensors, "each with a different scale, so the signals from the two can be compared for their differences and checked for accuracy." If one sensor fails, the check engine light goes on. If two fail, the engine goes into idle-only mode.
Asked if this kind of redundancy is built into all of Toyota's vehicles, spokesman John Hanson responded by email, "Yes it is, yes it is, yes it is."
According to Harvey Steele, vice president of Xilinx Inc., an electronics supplier to the Mercedes S Class, among others, "I'm not aware of any driver assistance areas that do not have fail-safe and/or redundancy built in. But it might not be to the level of an airplane, where there might be three or four levels of redundancy."
And according to Cheryl Kilborn, a spokesperson for major auto supplier Bosch, "Automotive electronics are always designed to be self-testing for safe functioning and to revert to fall-back mode if an error is detected." In the case of an engine control unit, she said, this could mean the car going into a "limp home" or "idle-speed" function. And that's what's supposed to happen in the Camry.
All this makes it very hard to explain exactly what is happening with these cars. Yesterday, the president of Toyota, grandson of the company's founder, apologized for the trauma inflicted on consumers. "I deeply regret that I caused concern among so many people," he said. And Akio Toyoda added that he's not trying to minimize the situation. "I believe that what is happening now is a very big problem," he said Friday. "We are in a crisis." He won't get an argument from this quarter.
Flickr photo/Stradablog