The head of Toyota Motor Corp.'s U.S. sales unit admitted Tuesday there were mistakes in the automaker's response to complaints over problems with its vehicles but vowed in prepared testimony for the first of a series of U.S. congressional hearings to build safer cars.

Toyota Motor Sales U.S.A. Inc. President Jim Lentz also reiterated that the carmaker's electronic throttle control system is not behind the sudden acceleration of some Toyota and Lexus vehicles, an issue thought likely to be the focus of the hearings.

"It has taken us too long to come to grips with a rare but serious set of safety issues," Lentz said in a prepared statement made available prior to his testimony. "We acknowledge these mistakes, we apologize for them and we have learned from them."

The congressional hearings were to kick off Tuesday morning with a session at a subcommittee of the House Energy and Commerce Committee, where Lentz and U.S. Transportation Secretary Ray LaHood were to testify.