Some owners of the 2010 Prius have reported their brakes do not always engage immediately when they press the brake pedal, or that the brakes have an inconsistent feel. The National Highway Traffic Safety Administration said it would assess the scope of the problem and the safety risk to about 37,000 cars that could be affected.

The investigation comes as safety questions surround Toyota, which has already issued broad recalls for millions of its best-selling vehicles, including the Corolla and Camry, because of gas pedals that can become stuck.

U.S. officials have blessed Toyota’s solution to that problem, a small piece of steel designed to eliminate excess friction in the pedal mechanism, but have criticized Toyota for being too slow in responding to customer complaints.

Asked whether Toyota would recall the 2010 Prius, spokesman Brian Lyons said: “It’s too soon to call at this point. We will, of course, fully cooperate with NHTSA in that investigation.”

The Prius trouble comes as Toyota service shops around the country work to handle gas pedal repairs. Dealers said they had heard little about any issue with Prius brakes or whether any fix was planned for cars already on the road.

Toyota was one of the first companies to mass-market a hybrid that combines an electric motor with a gas engine, introducing the Prius in Japan in 1997 and to the world in 2001. Its high gas mileage made it popular among environmentally conscious drivers, especially when gas prices spiked two years ago. 

But the complexity of the Prius, a highly computerized car, has led to problems in the past. In 2005, the company repaired 75,000 of them to fix software glitches that caused the engine to stall. It has also had trouble with headlights going out. 

In the case of the gas pedal problems, Toyota has insisted the trouble is mechanical, not electronic. 

For the Prius brakes, Mike Omotoso, senior manager of global powertrain for J.D. Power & Associates, said the culprit is a software glitch in the computer that controls the brakes. 

The problem, he said, occurs as the Prius switches between using its electric motor and internal combustion engine to power the car. Whichever motor is powering the car also runs the brakes, he said, but the brakes give out momentarily in the transition. 

“It’s almost like a circuit interruption, because when you switch, there’s a short pause like a second or less,” he said. “The system should be reprogrammed where the braking power is applied for a split second longer” on the motor that was powering the car, he said. 

Separately, Ford Motor Co. plans to fix 17,600 Mercury Milan and Ford Fusion gas-electric hybrids because of a software problem that can give drivers the impression that the brakes have failed. The automaker says the problem occurs in transition between two braking systems and at no time are drivers without brakes.

Most of the recalled vehicles are in the US, with smaller numbers scattered across the globe.

The brake pedal recall affects 179,000 vehicles in the US and about 26,000 in the Middle East, Canada, Russia and several other countries.

A pin in the pedal assemblies on certain 2008 to 2010 Nissan Titan pickups, Infiniti QX56 and Nissan Armada Sports Utility Vehicles, and some 2008 and 2009 Nissan Quest minivans can come loose and cause reduced braking force, Nissan said Tuesday in a statement.

No injuries or crashes have been reported, the company said. Customers with loose brake pedals should contact their dealer.

Nissan blamed the problem on a manufacturing defect by a parts supplier. Dealers will inspect the vehicles for loose pins and repair them if necessary.

The company said in a statement that all vehicles now on sale do not have the problem.

Nissan also is recalling 419,000 vehicles in the US and 53,000 elsewhere because gas gauges can show fuel left in the tank when it’s actually empty.

The recall affects 2005 through 2008 Nissan Titan, Armada and Infiniti QX56s as well as Nissan Frontier pickups and Pathfinder and Xterra SUVs produced between January and March 2006 and between October 2007 and January 2008.

Due to a problem with a sensor inside the fuel tank, the gauges can show gas tanks a quarter full when they are in fact empty.

Nissan suggests keeping a half-tank of gas in the vehicles until the gauges can be repaired, eliminating the risk of running low on fuel.

Owners of vehicles in both recalls will be notified when to bring their cars and trucks in for repairs. In materials distributed to dealers, Nissan said the brake pedal recall begins on March 22, while the fuel-gauge recall will take place in two groups, one beginning March 22 and the other starting in April.

About 130,000 vehicles are covered by both recalls.