Waymo is rolling out a software recall across nearly 4,000 self-driving vehicles after regulators found its robotaxis could mishandle flooded roads, raising fresh questions about how autonomous systems cope with extreme weather.

Documents filed with the National Highway Traffic Safety Administration describe a scenario in which Waymo vehicles, using both its fifth- and sixth-generation autonomous driving stacks, encountered waterlogged lanes they could not safely cross. Instead of coming to a complete stop or rerouting, the robotaxis slowed but continued moving toward the flooded area, creating a potential safety risk.

The recall covers 3,791 vehicles operating in roughly a dozen U.S. cities, offering a rare public snapshot of the scale of Waymo’s commercial fleet. The company has pushed an initial over-the-air update that adds new constraints on when and where its vehicles can operate, particularly on higher-speed roads where flash flooding is more likely.

According to the NHTSA filing, the update imposes restrictions “at times and in locations where there is an elevated risk of encountering a flooded, higher-speed roadway.” Waymo says it is refining how its system interprets and responds to “untraversable flooded lanes,” while it continues to work on what regulators describe as the “final remedy” for the defect.

The flooding issue came into sharp focus in central Texas, where heavy rains created hazardous conditions for autonomous vehicles. In one widely scrutinized incident in San Antonio, an empty Waymo robotaxi was swept away after entering floodwaters, prompting the company to pause operations in the city while it reviewed its weather and routing logic.

Waymo characterized the move as a voluntary software recall and said it is layering in additional safeguards, including tighter rules for operating during intense rain and limiting access to areas prone to flash flooding. The company emphasized that the fix is being delivered remotely, without requiring owners or riders to bring vehicles into service centers.

This is the latest in a series of recalls for Waymo’s driverless fleet, following previous software corrections related to low-speed collisions with stationary objects and improper behavior around school buses. Together, the actions underscore how autonomous driving companies are being forced to iterate in public, with regulators and the public scrutinizing how these systems respond not just to traffic, but to the unpredictability of the natural world.