Is an electronic error adding to Toyota’s woes?

Could there be a ghost in some of Toyota's high-tech machines?

That's the question hanging over the leading Japanese automaker even after the recall of more than six million vehicles since October. The stakes are huge for Toyota's business future and the safety of its increasingly skittish customers.

Toyota first blamed loose floor mats for instances of unintended acceleration that one analysis has linked to more than 800 crashes and 19 deaths since 1999. Last month, the company added that some of its vehicles also could speed out of control because of sticky gas pedals.

But Tuesday, U.S. officials joined outside experts in suggesting that a third factor may be to blame in some cases: a so-far-unidentified failure in the vehicles' electronic throttle systems.

Toyota Motor Corp. and the National Highway Traffic Safety Administration (NHTSA) say they have explored that possibility and come up dry.

"We have investigated every type of possible interference with the electronic throttle controls and have found nothing - nothing with the electronics or the computers - that could lead to unintended acceleration," said Toyota spokeswoman Cindy Knight. "We are confident we have identified the two separate mechanical issues and developed effective mechanical remedies."

But outside experts on automobiles, computers, and electronics welcomed a renewed focus on the possibility that something other than errant floor mats and sticky pedals could be at work.

"There are all kinds of ghosts in systems where something surprising happens," said Peter G. Neumann, an expert on computer-related risks and principal scientist at SRI International, a nonprofit research institute in Menlo Park, Calif. "It's quite plausible there could be an electronic component to this."

Software and hardware failures have long plagued complex devices that mix electronic and mechanical systems, Neumann said. Years ago, for example, citizens band radio signals were shown to have interfered with some truckers' cruise-control systems. Heart pacemakers were accidentally reset by microwaves.

"In one case, an antitheft device reset a pacemaker to 140 beats a minute," Neumann said.

The sheer rarity of Toyota's reported failures makes them much harder to diagnose, a difficulty that could be compounded if a software failure were partly at fault.

"With digital systems, all you need is for a 1 to be a 0, and that only has to happen once within millions of vehicles driven billions of miles," said Jeff Bartlett, deputy online editor at Consumer Reports.

To get a better handle on the acceleration problem's scope, the magazine recently examined the nearly 6,000 incidents reported to NHTSA in 2008. It found 166 complained of unintended acceleration in 22 brands of vehicles. Bartlett said Toyota vehicles were identified in 41 percent of the complaints, which he called "dramatically disproportionate" to the company's 16 percent share of that year's auto market.

Knight said Toyota had long known of the risks of electronic failure and had taken extensive steps to guard against potential interference from radio waves, microwaves, and other electromagnetic fields.

"Anything that could interfere with the transmission of an electronic signal has been thoroughly investigated," she said.

As Toyota's problems draw scrutiny, attention has increasingly focused on its electronic "drive-by-wire" system, which replaces the traditional mechanical linkage between a gas pedal and engine with an electronic interface.

European carmakers first developed drive-by-wire systems, based on similar systems in aircraft. Knight said Toyota introduced drive-by-wire in 2002, and now uses the system in all its vehicles. "It's standard in the industry now," she said.

Gabriel Shenhar, senior auto test engineer at Consumer Reports, said the systems use a medley of sensors, actuators, and microprocessors to translate pedal pressure into engine speed as effectively as mechanical systems.

Such systems offer numerous benefits, Shenhar said, including the ability to better integrate throttle, braking, and other controls more seamlessly in cars equipped with high-tech traction-control or stability-control systems.

Could something in the software or electronics fail?

"Anything electronic, anything computerized, is a function of outputs and inputs. If someone programmed something that's a little off-kilter, then you're going to see that," he said. "That's not to say that there's more of a chance of that than anything going wrong with a mechanical system."

There is no question that the new systems pose unexpected challenges. Toyota got another taste of that this week as a new, apparently minor problem drew complaints from drivers of 2010 Priuses who reported an odd sensation after hitting potholes.

Toyota is investigating the complaints, but Knight said they apparently occurred when a wheel goes momentarily airborne and loses traction, which then activates the car's stability-control system.

Ironically, if Toyota's problem might be partly electronic, its solution may be, too: a new braking-override system sometimes referred to as a "smart pedal."

Knight said Toyota would soon begin installing them in new Lexus ES350 and Camry sedans, as well as recalled models of the same cars, but that it was unclear whether other recalled vehicles would get the upgrade. "All our new vehicles will have the override system by the end of this year," she said.

The smart pedal essentially will give the brakes priority over the throttle. If a driver is braking at the same time somebody or something is calling for more gas, the car will come to a stop.

Knight said the smart brake was not intended to address the problems identified in the recalls, which she said would be fixed as soon as possible in all cars. "It's just to provide an extra measure of confidence," she said.