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Concerns about Brexit -- and about defective shifters in vehicles like this Jeep Grand Cherokee -- hit Fiat Chrysler shares hard on Friday morning. Image source: Fiat Chrysler Automobiles

What: Shares of Fiat Chrysler Automobiles (NYSE:FCAU) were moving quickly on Friday morning, and not in a positive way: At 11:00 a.m. EDT, the Italian-American automaker's shares were down 11.2% to $6.39 in trading in New York.

So what: Concerns over the British vote to leave the European Union hit many companies hard on Friday morning, but FCA was hit harder than most of its peers. That may be surprising to Americans who tend to think of Fiat Chrysler as mostly "Chrysler," but the Fiat side of the house has a major presence in Europe, along with a heavy debt load that could leave it vulnerable in a recession.

If the Eurozone were to slide into recession, Fiat (and Fiat Chrysler) would be hit hard, adding risk to a balance sheet that is already considerably weaker than those of most rivals.

There's more: FCA is also dealing with an ongoing recall that has the potential to get messy and expensive. An electronic automatic-shifter design used in many of the company's vehicles is confusing to use: Putting the vehicle in "park" requires holding the shifter in reverse for several seconds. If "park" doesn't engage, the vehicle can roll away after it's shut off.

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FCA's electronic shifter, shown here in a Dodge Challenger, has been blamed for a series of accidents. Image source: Fiat Chrysler Automobiles

The shifter may have been a factor in the recent death of Star Trek actor Anton Yelchin, who was crushed against a gate by his Jeep Grand Cherokee after it apparently rolled down his driveway. FCA recalled 1.1 million vehicles with the shifter in April. At that time, the defect was linked to 41 injuries, 212 crashes, and 308 reports of property damage. More vehicles have been added to the recall in recent days.

Now what: The biggest factor in Friday's sell-off is probably just the uncertainty around both issues. FCA is working through the process of the shifter recall, and we'll have to wait and see if a class action suit by owners gets traction before we can guess how much it'll cost.

As for "Brexit," it's also hard to say how badly it'll hurt FCA, given the many economic unknowns arising from the decision. For investors who hold FCA shares, I recommend that you take my colleague Morgan Housel's advice: For now, sit tight.

John Rosevear has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.