Porsche enthusiasts have been rolling up to dealerships lately only to be disappointed: they won’t be sold the specific car that they’d had their eyes on. Those vehicles feature something called the Sport Chrono Package—and that package is letting out more emissions than is acceptable.

This great reporting comes from Kristen Lee over at , who tracked down this story through emails from concerned Porsche buyers. From the article:

The Sport Chrono Package was an option you could get on your Porsche that let you pick different electronic driving modes. “Normal” was for everyday driving, “Sport” was designed for the twistier roads, and “Sport Plus” was meant for extreme driving, as you would do on a racetrack.

But, as Porsche recently discovered during its routine review, there was a slight hiccup in the plan. When driven in “Sport Plus” mode, certain Sport Chrono Package-equipped cars built within a specific time frame emitted more nitrogen oxide than permitted.

That said, even the Sport Plus mode could occasionally produce a legal amount of nitrogen oxide, and not all cars feature the issue, but it’s unclear as to why it can produce more or less depending on the situation. Porsche confirmed to Business Insider that it issued a stop-sale of certain models in November 2020: the 911, Boxster, Cayman, Cayenne, and Panamera models from 2012-2016.

“Not every model line we’ve tested is affected,” a Porsche spokesperson told Lee. “So, it really goes down to us testing every model derivative. We’re being cautious.”

Porsche is trialing a software update that should rectify the exhaust emissions problem, at which point people my be able to buy them again. But with the currently confusing nature of the problem, it makes more sense to halt the sale of potentially problematic models until a clear answer is found.

As it stands right now, it doesn’t sound like any of the newer Porsche models are impacted.