Tesla is recalling over 1.8 million vehicles in the United States due to risk of software failure to detect an unlatched hood, the national auto safety regulator said today.

An unlatched hood could fully open and obstruct the driver’s view, raising the risk of a crash, the National Highway Traffic Safety Administration (NHTSA) said.

Tesla has started rolling out an over-the-air software update to fix the issue, the NHTSA said. The updated software detects an open hood and alerts drivers of the situation.

The recall affects certain 2021-2024 Model 3, Model S, Model X, and 2020-2024 Model Y vehicles, the regulator said. The vehicles, Tesla said, were equipped with a hood latch produced in China by Magna Closures Co Ltd.

The company said it began investigating customer complaints of unprompted hood opening instances in certain Model 3 and Model Y vehicles in China in March, and initiated a latch hardware recovery and in-service vehicle inspection.

While fewer such events occurred in Europe and North America, Tesla said it began engineering studies in the regions to inspect hood latch assemblies last month and decided to issue a recall earlier this month.

The recall is Tesla’s biggest since December when it had issued a recall covering 2.03 million U.S. vehicles – or nearly all of its cars on U.S. roads at the time – to install new safeguards in its Autopilot system.

However, following reports of 20 crashes involving vehicles that had the new Autopilot update, the NHTSA has opened a probe, saying it had identified “several concerns” regarding the recall.

Tesla last week posted its worst quarterly profit margin in more than five years, underscoring the EV maker’s struggle to revive auto sales amid a slowdown in demand.