The United States Department of Transportation’s Office of Defects Investigations (ODI) has opened a preliminary investigation into an estimated 1,720,768 Honda SUVs. The office will look to determine whether a manufacturing flaw has led to complaints of seizing rear differentials that leave drivers without power on the highway.

The organization reports that it has received complaints relating to the model year 2018-2022 Honda CR-V and HR-V. The ODI has received several field reports in which drivers allege that they suddenly lost motive power at highway speeds with no warning.

A leak in the differential seal appears to be at the heart of the problem, per the field reports, leading to a scenario in which the rear differential locks up, causing the SUV to grind to a halt. Additionally, that may be leading the driveshafts on these vehicles to fracture, leaving the vehicles almost entirely immobile, and requiring them to be towed.

Read: 1.7 Million Honda Vehicles Under Investigation After Complaints About Automatic Emergency Braking Incidents

The issue has not yet led to a recall, but the ODI says that it is opening this preliminary evaluation in order to determine the scope and severity of the problem and to fully assess its consequences, as relates to the safety of the vehicle occupants.

Although the ODI documents do not explicitly state it, the fact that the rear differential is the one locking up would suggest that the affected vehicles are all-wheel-drive models. The office has not revealed how many incident reports have been filed, but all were submitted as Early Warning Reports and the number remains “confidential,” per ODI documents.

The ODI has opened more than 20 investigations into potential safety defects this year, The Wall Street Journal reports. This, however, is among the largest so far in 2022, by total vehicle count.

In addition to this, the model year 2017-2019 Honda CR-V and the model year 2018-2019 Honda Accord, are the subject of an ongoing investigation relating to their automatic emergency braking system. The office has received 270 reports of phantom braking and, in total, 1.73 million vehicles are included in the scope of its investigation.