The National Highway Traffic Safety Administration (NHTSA) has opened a probe into Ram trucks with diesel engines, following up on reports of a problem with the high-pressure fuel pump. The problem could cause stalling and loss of power while traveling at speeds above 25 mph.

The reported problem could affect 604,651 2019–2020 Ram 2500, 3500, 4500, and 5500 trucks with the 6.7-liter Cummins turbo-diesel engine.

So far, NHTSA has received 22 complaints about the issue and two field reports. The agency has not yet issued a recall. The National Highway Traffic Safety Administration (NHTSA) announced today that it’s opening an investigation into the high-pressure fuel pump failure on some heavy-duty Ram trucks.

The problem, described in 22 consumer complaints so far, is that the trucks could stall and become immobile while traveling at speeds over 25 mph. The problem, NHTSA’s report says, could lead to “permanent disablement of the vehicle.”

NHTSA could issue a recall as a result of the investigation. According to NHTSA and a report today by the Detroit News, Stellantis (then Fiat Chrysler) was aware of the issue much earlier and put out a warranty bulletin in November 2019 about the problem, asking dealers to “collect, monitor, and correct quality issues” with the trucks’ high-pressure fuel pumps.

NHTSA said it is opening the investigation to “further assess the scope, frequency, root cause, and potential safety-related consequences of the alleged defect leading to stall/loss of motive power.” If a recall follows later, truck owners can expect to be notified and asked to bring their vehicle to a dealer for a fix. In the meantime, owners of potentially affected Ram heavy-duty trucks can check the NHTSA recall site for updates on the investigation.