US regulators launched a preliminary investigation into reported steering problems on the Corolla sedan on Wednesday as Toyota Motor Corp faced questions from US lawmakers on whether it had ignored red flags on safety before a wave of vehicle recalls.

The National Highway Traffic Safety Administration has received more than 150 complaints about possible steering problems in 2009 and 2010 Corolla models, a US government official said.

A 2010 Toyota Corolla automobile is displayed at a Toyota dealership in Daly City, California, February 17, 2010. US auto safety regulators said on Wednesday they are continuing their review of steering complaints in Toyota Motor Corp vehicles. A National Highway Traffic Safety Administration official told Reuters that the informal review of consumer complaints would continue to see whether a full investigation was warranted.

The agency began reviewing complaints about the Corolla models last week and on Wednesday determined that the evidence warranted opening a preliminary evaluation, according to the official who asked not to be named because the plan has not been announced.

The Corolla is Toyota's second-most popular model in the US market, behind the Camry.

Such preliminary investigations are a common step by NHTSA and are often closed before being upgraded to a second-stage investigation or prompting a vehicle recall.

But the move comes at a time when Toyota and US safety regulators are under intense scrutiny for their handling of safety complaints related to unintended acceleration in Toyota vehicles going back a decade.

Toyota spokeswoman Cindy Knight said the automaker was aware of the Corolla steering complaints and would "cooperate fully with NHTSA's investigation."

Toyota is being challenged by US lawmakers to answer the criticism that the company's practice of tightly controlling key decisions in Japan had contributed to its deepening problems in the US market and criticism that it has not been forthcoming with safety regulators.

In a move that raised the stakes for a pair of congressional hearings next week, Toyota President Akio Toyoda said he would send North America chief Yoshimi Inaba to testify instead of making an appearance himself.

Toyoda, grandson of the 77-year-old automaker's founder, said he believed Inaba was the logical choice to testify.

"I have full confidence in the management of Toyota Motor North America, led by Mr. Inaba, and I believe he is the best placed to testify," Toyoda told reporters at his third news conference in two weeks.

The statement by Toyoda came a day after the automaker moved to cut production in the United States and NHTSA opened an investigation into whether it had acted in a timely way in responding to safety complaints. ID:nN16223813

A series of vehicle recalls since January have damaged Toyota's once-vaunted reputation for quality and safety. Up to 34 crash deaths have been blamed on unintended acceleration in Toyota vehicles since 2000, according to complaints filed with US regulators.

Toyoda faces a deepening crisis just seven months into his tenure as the automaker's chief. He said Toyota may have grown too fast in recent years, outstripping its ability to ensure that vehicle quality standards were maintained.

Two congressional panels plan hearings next week to look into Toyota safety issues. The US House Energy and Commerce panel moved its hearing to Tuesday instead of Thursday. The US House Committee on Oversight and Government reform is scheduled to hold a hearing on Wednesday.

The top Democrat and Republican on the oversight panel asked major insurers for information they may have provided to US safety regulators on reports of unintended acceleration in Toyota vehicles.