As Toyota Motor Corp. faced a possible recall of its best-selling Prius hybrids over brake-related problems both in the Unites States and Japan, safety concerns that were largely considered an overseas issue have quickly spread to the home market.

In a fresh blow to its already faltering reputation for quality, complaints about braking problems in the latest model of the gasoline-electric hybrid have been filed at the transport ministry and Toyota dealers across Japan.

Such defects, experts say, may be traced to the fact that an increasing number of cars carry sophisticated electronics and that carmakers are consolidating these units to achieve lower costs.

“There is no doubt it is a severe blow to Toyota, which has focused on eco-friendly cars,” said Yasuo Tsuchiya, a visiting professor at Meiji University.

In particular, hybrids are outfitted with bigger computers than other cars, so they are more prone to technological glitches, added Tsuchiya, who specializes in the auto industry’s global management.

“Cars made these days are loaded with a number of high-tech electronic units, while the software is outsourced. Many software makers participate in the manufacturing process, which makes it hard for automakers to work in close cooperation with them,” he said, adding other automakers could face similar woes.

Toyota said Thursday it had made corrections to the software for the Prius antilock braking system in January in response to brake-related problems on bumpy or icy roads but didn’t issue a recall.

Experts say the quality control problem could become more serious if the claims made in the United States are found to stem not only from floor mats or defective gas pedal parts, but from the more crucial electronic system.

“If reported unwanted accelerations are due to reasons other than floor mats, say electronic control systems, it would be extremely difficult and complicated to find the cause,” said Kunihiko Fujiki, consultant for Fujiki Business Research Office. Fujiki dealt with parts procurement at Nissan Motor Co. for more than 30 years.

In that case, the problem would be much larger and include a gas pedal sensor or, more importantly, an engine control unit that controls combustion.

The sensor is supplied by Japanese carmakers, while the ECU is probably supplied by either carmakers or Toyota itself, he said.

Toyota insisted Thursday the gas pedal glitch has nothing to do with its electronic system.

“We believe the electronic throttle does not have a glitch, as far as we know,” Hiroyuki Yokoyama, managing officer in charge of quality control, told a news conference in Tokyo.

Experts meanwhile said the automaker also lacks an effective global strategy.

Toyota’s eroding quality control stems from too rapid expansion abroad and global price competition, which have forced the auto giant over the last decade to abandon its long allied group parts makers, including Denso Corp., for new overseas partners that cost much less, experts said.

Toyota’s reputation for quality rests on its “integrating” parts makers into its quality control process by producing trial parts and running countless tests, which it has long done with trusted partners.

“The advantage of keiretsu is that Toyota and its affiliated firms develop and produce their products together,” Tsuchiya said.

“But Toyota has had to select less costly parts makers beyond the keiretsu group. As a result, the systematic manufacturing ability has weakened,” he said.

He pointed out that in 2005, when CTS Corp. — the maker of the gas pedal parts involved in the latest recalls — started to supply parts to Toyota, the carmaker, under former President Katsuaki Watanabe, was set to become the world leader and accelerated global production.

Rivals Nissan and Honda Motor Co. also face the threat of massive recalls.

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