Ford is recalling about 3,100 F-Series ambulances because the engines can stop unexpectedly.
The F-350, F-450 and F-550 Super Duty ambulances have 6.7-litre diesel engines. They're from the 2011 and 2012 model years.
Ford says a faulty exhaust gas temperature sensor can cause the engines to stop and not be restarted for at least an hour. The company says it has no reports of the problem affecting patient care.
Most of the ambulances were sold in the U.S., with some in Canada and other countries.
Dealers will replace the sensor.
Ford says the problem could occur on non-ambulance versions of the same trucks, but the company isn't recalling them. Drivers will get a warning and enough time to safely pull off the road before the engine shuts down.