U.S. auto safety investigators have determined that electronic gear shifters in some newer Fiat Chrysler SUVs and cars are so confusing that drivers have exited the vehicles while they are in gear, causing 121 crashes and 30 injuries.

The National Highway Traffic Safety Administration has doubled the number of vehicles in the investigation to more than 856,000. But it stopped short of calling for a recall.

The probe now covers 2014 and 2015 Jeep Grand Cherokees and 2012 through 2014 Dodge Charger and Chrysler 300 sedans with 3.6-liter V6 engines. The safety agency says in documents posted Monday that it’s upgrading the investigation to an engineering analysis, which is a step closer to a recall.

Fiat Chrysler says it’s cooperating with the probe.

(AP)