Mexico City - Mexico's Profepa environmental protection agency on Monday fined German automaker Volkswagen's local unit just over 168 million pesos (around $9 million) for selling 2016 model vehicles that lacked the corresponding environmental compliance certificates.

Volkswagen Mexico was fined for importing and selling 45,494 Audi, Bentley, Porsche, Seat and Volkswagen vehicles in Mexico, Profepa said in a statement.

In a December 2015 inspection, the agency discovered that those vehicles lacked two NOM environmental compliance certificates, one that establishes the maximum allowable level of total hydrocarbon, carbon monoxide, nitrogen oxide and particles from new cars' exhaust pipes and another that sets the maximum allowable level of noise and the measurement methodology.

Profepa said the fine was separate from an investigation being conducted in Mexico over the Volkswagen defeat device scandal.

In September of last year, Environment Secretary Rafael Pacchiano said Mexico would review Volkswagen's emissions certificates for diesel engine vehicles the automaker had sold in Mexico since 2009 to verify if they were in compliance with national standards.

That probe came after Volkswagen acknowledged that the defeat devices had been installed on nearly 500,000 2.0-liter diesel-powered Audi, Porsche and Volkswagen vehicles sold in the United States since 2008.

The U.S. Environmental Protection Agency accused the automaker last September of using the devices to dupe regulators.

The software on those engines detected when emissions testing was taking place and turned on emissions controls only when the vehicles were being operated in a test laboratory.

When those same vehicles were being driven under normal conditions, the controls were turned off and they spewed up to 40 times the United States' legally allowable amount of nitrogen oxide, which contributes to the formation of smog and acid rain.

The automaker said last September, after the scandal broke, that 11 million of its vehicles worldwide had been equipped with the defeat devices.