Japan's Toyota Motor on Tuesday said it would offer to repair a defective engine coolant pump on around 650,000 of its top-selling Prius models worldwide, in a move that it said was not a recall.
The world's largest automaker said it would "voluntarily" replace the pump controlling the temperature of the hybrid engine system, which if not working properly may lead to overheating.
However, the company said that the fault would not prevent the car from running and it had received no reports of accidents or injuries as a result of the problem.
Automakers often issue repair notices separately from official recalls filed with regulators if they see no safety risk.
"This is a 'customer satisfaction campaign,' which is a voluntary action of the company unlike legally-bound recalls," said Toyota spokesman Paul Nolasco.
"Even if overheating occurs, it would not stall the vehicle but would result in lower power," he said, adding there had been no reports of accidents resulting from the issue.
The action covers 2004-2007 models and includes around 390,000 vehicles in North America and 180,000 in Japan. Owners are invited to submit vehicles for repair, the company said.
The announcement comes as the automaker works to rebuild an image marred by more than 12 million safety recalls in the past year over unintended acceleration, engine, steering and brake problems.
The crisis prompted US congressional investigations as Toyota was hit with a record 16.4 million dollar fine to settle claims it had hidden accelerator pedal defects blamed for dozens of deaths. It still faces lawsuits in the United States.
Last month Toyota announced a global safety recall of about 1.5 million vehicles to fix a brake fluid leak that it warned could gradually diminish braking performance.
Analysts say Toyota has become more aggressive in catching possible defects as part of a campaign to improve its consumer image, but warn that continued frequent recalls continue to damage its branding as a quality carmaker.
Toyota has sold more than two million petrol-electric Prius vehicles worldwide since the launch of the first version in 1997. It has been Japan's top selling car for more than a year.