In the nearly five months since it launched a string of recalls to stop its cars from accelerating out of control, Toyota Motor Corp. has been adamant about one thing: It's not the electronics.
Company officials first put the blame on floor mats that could entrap the accelerator, later amending that to include gas pedals themselves that could stick.
But they have vigorously asserted that there is no evidence of a glitch in the electronics or software that could cause cars to malfunction, a "ghost in the machine."
Some independent safety experts, congressional investigators and others are just as certain that the risk of an electronic flaw is being dismissed by Toyota without an adequate examination.
The causes of unintended acceleration remain under investigation, but an admission by Toyota that sudden acceleration was caused by an electronic defect would be a devastating blow to the company's already damaged reputation for quality, say engineers, attorneys and experts in crisis management.
Compared with mechanical problems such as floor mats and sticky gas pedals, an electronic hardware or software glitch can be difficult to find, costly to fix and would open Toyota to a new onslaught of lawsuits, these people say.
"Every car accident that took place for years will suddenly be blamed on electronics," said Ted Frank, an attorney and founder of the Center for Class Action Fairness.
And considering the fact that every Toyota vehicle sold in the U.S. since the 2007 model year has an electronic throttle, with some models using the system dating to the 2002 model year, the number of potentially affected vehicles could reach into eight figures.
"It's a big potential problem for Toyota," Frank said.
Indeed, less than 24 hours after Toyota announced its recall of the 2010 Prius and Lexus HS250h last week, at least two suits alleging economic damages to owners of the hybrids had been filed against the automaker, adding to a pile of suits related to the recalls now numbering in the dozens.
Beyond its legal liability, Toyota's relationships with its customers could be further damaged by any finding that sudden acceleration is being caused by electronics, instead of floor mats or gas pedals, some say.
"Cars are moving computers, and the electronics are the very heart of the car," said Ian Mitroff, emeritus professor of USC's Marshall School of Business and a consultant on crisis management. Unlike a mechanical problem, like a sticking pedal, the fix is not easily understood, he said.
"It's the most scary component of all," said George Hoffer, an economist at Virginia Commonwealth University who moonlights as a consultant on recalls for automakers.
Toyota says it has repeatedly and thoroughly tested its vehicles, including their electronic throttle systems that replace traditional mechanical accelerator controls with sensors, wires and computers, with no finding.
In a letter to Rep. Edolphus Towns (D-N.Y.) that was released Friday, attorneys for the automaker said it had hired an engineering and testing firm to test its electronic throttle system. The firm, Exponent, based in Menlo Park, Calif., found that the system "did not exhibit any acceleration or precursor to acceleration, despite concerted efforts to induce unwanted acceleration," the letter said.
"There is simply nothing there to say electronic controls are causing the problems," said Bob Carter, general manager of Toyota's U.S. sales division, at the Chicago Auto Show last week. "We have exhaustively tested every scenario."
The National Highway Traffic Safety Administration, meanwhile, has opened a new investigation at the behest of Transportation Secretary Ray LaHood to determine whether electromagnetic interference could cause sudden acceleration, but has said it had never found evidence to support that theory.
But experts in electronics say that even the most thorough testing can fail to turn up computer problems, given the increasing complexity of automobile technology.
"It can be a tremendously difficult thing to spot," said Ronald Jurgen, an electrical engineer who edits the Automotive Electronics Reliability guidebook for the Society of Automotive Engineers.
He said that code errors in programs, electromagnetic interference or design problems in circuit boards could create issues that appear only in extremely rare instances.
"And when you can't spot it, it's just as dangerous and deadly as a major mechanical problem," Jurgen added.
So far, Toyota has proposed relatively low-cost fixes for the problems that cause sudden acceleration, such as a small shim for gas pedals that outside experts say probably costs a few pennies to produce.
But if an electronics problem is found, new microprocessors or new engine control modules could be a lot more expensive, aside from labor costs.