DETROIT (AP) — U.S. safety regulators are investigating brake problems in 90,000 late-model BMW cars.

The National Highway Traffic Safety Administration says the probe covers the 328i from the 2013 model year.

The government has received four complaints from drivers that it was difficult to brake the cars. Some reported increased stopping distances.

The agency says that in three complaints, dealers found problems with a vacuum pump.

No crashes or injuries have been reported.

Investigators will determine if the problem is large enough to warrant a recall.