BMW facilities in Austria and Germany have been searched by prosecutors in search of defeat devices.
According to a report in Automotive News, around 100 police and law enforcement officials raided the brand's Munich HQ and its engine plant in Steyr, Austria.
Prosecutors told the outlet "there is an early suspicion that BMW has used a test bench-related defeat device", in a statement.
BMW has outright denied the idea its cars are designed to circumvent emissions rules, and said the investigation hadn't found any "targeted manipulation" of regulations.
Since the now-infamous Volkswagen Dieselgate scandal broke in 2015, a number of other car manufacturers have been accused of gaming emissions regulations through software.
The US Environmental Protection Agency (EPA) filed a lawsuit against Fiat Chrysler Automobiles (FCA) in May 2017, alleging the company used a 'defeat device' in 104,000 vehicles fitted with its 3.0-litre EcoDiesel engine.
FCA announced plans to "vigorously defend" itself and denied any "deliberate scheme" to cheat, but the company faces fines and a major recall if it accepts a settlement offer from the US Department of Justice.
The EU competition watchdog is investigating a number of manufacturers over accusations of collusion surrounding diesel tests, based on concerns "several German car manufacturers may have violated EU antitrust rules prohibiting cartels and restrictive business practices".
In response to the fuels worsening image, FCA is reportedly planning to cull it from its line-up by 2022. Porsche has recently stopped production of the Macan S Diesel and Panamera Diesel, although a Cayenne Diesel is still on the way.