DETROIT » The government has expanded an investigation of fires that can start in the doors of several Toyota models, adding 600,000 Camrys and other vehicles to the probe.

The investigation now includes 1.4 million cars and SUVs from the 2007 to 2009 model years. When the inquiry began in February, it involved more than 800,000 Camrys and RAV4 SUVs from the 2007 model year.

Certain Camrys from the 2008 and 2009 model years, as well as some 2007 to 2009 Yaris subcompacts and all 2008 Highlander Hybrid SUVs, have been added to the investigation, the National Highway Traffic Safety Administration said Monday on its website. The vehicles were built from September 2006 through August 2008, the agency said.

So far, Toyota and the government have received 161 complaints of fires involving the vehicles. Nine people have been hurt, according to government documents.

All the vehicles use the same power window switch in the driver’s door. The switches can overheat and cause fires, the government said.

NHTSA has upgraded the investigation to a so-called engineering analysis, which can lead to a recall.

Owners of the Toyotas who smell smoke or feel heat in the doors should call their dealers or take them in for an inspection, Toyota spokesman Brian Lyons said. The company is cooperating with NHTSA in the investigation, he said.

Toyota’s Camry midsize sedan is the most popular car in the United States, and the RAV4 small SUV also is a big seller. In December, the 2012 Camry received a five-star safety rating from the NHTSA, the agency’s top rating.

Toyota’s reputation has taken a hit through the past three years due to a string of huge recalls that ballooned to more than 14 million vehicles worldwide. Millions were recalled for acceleration problems, and Toyota replaced floor mats that can trap gas pedals and pedal assemblies that can stick and cause cars to take off by surprise. After an exhaustive probe, U.S. safety regulators, aided by NASA engineers, found nothing wrong with Toyota’s electronic throttle controls.

Federal safety regulators also are investigating a similar fire problem in the doors of 2006 and 2007 Chevrolet TrailBlazer SUVs made by General Motors.

NHTSA posted documents Saturday saying that the GM probe also had been upgraded to a full engineering analysis. Originally the investigation covered more than 309,000 TrailBlazers from the 2006 and 2007 model years, but the government said that it’s up to nearly 342,000 vehicles.

NHTSA and GM have received 242 complaints about the problem, including 28 fires. No one has been hurt, according to the documents.