Toyota Motor will pay to fix about 650,000 Prius models worldwide for a coolant pump glitch that could cause the top-selling hybrid to overheat and lose power, the automaker said.

The repair campaign covers Prius cars for the model years 2004 to 2007. The bulk of the cars, or 378,000 units, are in the United States.

The Japanese automaker said it had not received any reports of accidents or injuries from problems with the pump, which circulates coolant for the hybrid system.

2010 Toyota Prius

Major automakers, including Toyota, often conduct repair campaigns that are separate from safety recalls filed with U.S. regulators in cases where they determine that a defect does not present a safety risk.

Toyota said the design of the electric water pump let air bubbles enter the system, slowing coolant circulation and allowing the hybrid's components to heat up.

The heating up of the components could trigger a warning light. If left unattended, the Prius could overheat and drop into a "fail-safe" mode where engine power would be reduced, Toyota said.

Toyota said it will begin notifying owners of the Prius repair campaign in the United States in early December.

The automaker has used a different pump design on the Prius hybrid since 2007 and uses a different type of pump for other hybrids, Toyota spokesman John Hanson said.

Toyota will cover the cost of the repairs, including more than $100 in labor for each Prius fixed at a U.S. dealership.

The repair campaign on one of the best-known Toyota vehicles comes at the end of a year in which the top global automaker has struggled to distance itself from a damaging series of recalls and concerns about its quality management.

Since last November, Toyota has recalled about 14 million vehicles worldwide, including about 11 million in the United States.