In a news release early Wednesday, the automaker said the electric power steering pinion-shaft attachment nuts could loosen and “over time, the customer will gradually notice significant increased steering effort when making a left turn.”
Toyota’s announcement did not mention any accidents, but when reached for comment, Brian Lyons, a Toyota spokesman, said the automaker received one unconfirmed report of a minor accident. The company described the recall as voluntary, but under federal regulations, once a manufacturer was aware of a safety problem it must inform the National Highway Traffic Safety Administration within five business days of its plan for a recall.
The automaker has been looking into the problem for almost four years, according to a document filed with the safety agency, in which Toyota said it received a field technical report in August 2007 that the steering wheel locked up on a first-generation Japanese-market Prius.
Toyota told the agency it discovered that the locking nuts were loose and began investigating how the condition was created. It received sporadic reports of other vehicles with such problems, but it was not until late in May 2011 that brand engineers determined the cause and concluded a recall was necessary.
The problem is related to tightening and lubricating grease from the rack-and-pinion assembly reaching the nuts. Because of differences between the right- and left-hand-drive models, the steering wheels on the Prius sold in the United States would not stick, although there could be a significant increase in driver effort, the company said.
In 2000, Toyota recalled about 1,700 of its 2001 Prius models for a power-steering problem. The automaker told the safety agency at the time that a problem with the torque sensor might cause a “higher than normal” steering effort. Wednesday’s announcement is not related to the 2000 action, Mr. Lyons said.
The agency has several dozen complaints from owners about problems with power steering on 2001-2 Priuses.
One owner wrote that the power steering on his 2001 Prius failed at 13,396 miles, 65,427 miles and 105,000 miles. He said Toyota paid the first two times, but on the third failure the automaker covered parts but not labor.