Shares of Toyota Motor edged higher on Thursday despite news of a US probe into another Toyota vehicle for possible safety problems that helped deter investors from reacting fully to the carmaker's plan to improve its safety systems.

US regulators launched a preliminary probe on Wednesday into reported steering problems in Toyota's Corolla sedan, the company's second-most popular vehicle in the US market after the Camry sedan.

Also on Wednesday, Toyota confirmed a plan to install a brake override system in all new vehicles, after deadly acceleration and braking problems prompted it to recall 8.5 million cars.

The company also said it was looking into complaints about the steering systems of 2009 and 2010 Corolla models but denied it was considering recalling the vehicles at this stage.

"Our internal studies have shown that drivers have complained about a change in steering response versus the older Corollas possibly due to a switch from a hydraulic power steering system to an electronic one," Toyota's quality chief, Shinichi Sasaki, told a news conference.

Studies have yet to make clear if the problem is due to the steering, tyres or another part, he said, adding that there would only be a recall if the issue was deemed to be a safety breach.

On Thursday in Tokyo, Toyota spokeswoman Ririko Takeuchi said it still had not been informed officially by US regulators of any formal probe into the Corolla.

By midday in Tokyo shares of Toyota were up 0.2 per cent at 3,385 yen ($37.22), performing in line with a rise in the Nikkei average.

"Both Toyota's plan and the probe into the Corolla are mainly in line with the direction of developments investors expect to continue for Toyota in the near future," said Kazuhiro Takahashi, general manager of investment strategy at Daiwa Securities Capital Markets.

"Investors, though not overly optimistic, are welcoming Toyota's efforts to move away from behaviour that has hurt trust in it, while they expect political pressure to remain against Toyota in the US in the near term," he said. – Reuters