Waymo is recalling 3,988 of its autonomous robotaxi vehicles after the National Highway Traffic Safety Administration identified a software issue that caused the cars to behave unpredictably near active construction zones, the company and the agency confirmed on Friday.

The recall covers Waymo’s entire active fleet, which operates across San Francisco, Los Angeles, Phoenix, and Austin. The flaw involves how the vehicle’s perception software classifies and responds to atypical road configurations, particularly narrow lane patterns, temporary barriers, and vehicles in construction zones that change position more frequently than stationary objects.

NHTSA opened the investigation in April after receiving 23 complaints involving Waymo vehicles braking sharply or making unexpected steering corrections in construction areas. Two incidents involved minor collisions — one in San Francisco in March where a Waymo vehicle made contact with a construction barrel while navigating a lane merge, and one in Phoenix in April where a vehicle stopped abruptly on a highway ramp due to a misclassified traffic cone, causing a following vehicle to make an emergency stop.

No injuries were reported in connection with either incident. Waymo said both had already been flagged by its internal safety team before the NHTSA inquiry began and that the software involved had been updated following each event. NHTSA said the recall was nonetheless necessary because the updated software had not been formally documented as a safety-related fix at the time it was pushed to the fleet.

Waymo said the recall would be addressed through an over-the-air software update that the company described as already completed for most of the fleet. Unlike traditional automotive recalls, no vehicles need to be brought to a physical service center. The company said its autonomous vehicles would continue operating during the update process.

The recall is the largest in Waymo’s history by vehicle count. A previous recall in 2024 covered 672 vehicles over a separate issue involving the cars’ response to emergency vehicles. That recall was also resolved with an OTA update.

Waymo’s chief safety officer said in a statement that the company welcomed the oversight process and remained committed to transparency with regulators. The statement did not acknowledge any fault in the original software design and characterized the recall as a documentation matter rather than a fundamental safety failure. Critics of autonomous vehicle deployment said the episode showed that existing regulatory frameworks were not designed for software-first transportation products.

The recall comes during a critical period for the autonomous vehicle industry. Waymo’s primary competitor, Tesla‘s robotaxi program, launched in June in Austin and has received regulatory attention of its own. A third company, Zoox, is expected to begin commercial operations before the end of the year. NHTSA has said it is developing new guidelines specifically for over-the-air software safety recalls in autonomous vehicles.

Consumer advocacy groups said the recall underscored the need for stronger pre-deployment testing requirements in construction zones, which present some of the most variable and unpredictable conditions on public roads. NHTSA’s recall database shows the Waymo case is among the first to specifically cite construction zone behavior as the trigger for a recall in the autonomous vehicle category.

Waymo said it expected to submit final documentation of the software update to NHTSA by June 30, completing the formal recall process within the agency’s required timeframe.