Last year, two Waymo robotaxis in Phoenix “made contact” with the same pickup truck that was in the midst of being towed, which prompted the Alphabet subsidiary to issue a recall on its vehicles’ software. A “recall” in this case meant rolling out a software update after investigating the issue and determining its root cause.

In a blog post, Waymo has revealed that on December 11, 2023, one of its robotaxis collided with a backwards-facing pickup truck being towed ahead of it. The company says the truck was being towed improperly and was angled across a center turn lane and a traffic lane. Apparently, the tow truck didn’t pull over after the incident, and another Waymo vehicle came into contact with the pickup truck a few minutes later. Waymo didn’t elaborate on what it meant by saying that its robotaxis “made contact” with the pickup truck, but it did say that the incidents resulted in no injuries and only minor vehicle damage. The self-driving vehicles involved in the collisions weren’t carrying any passenger.

After an investigation, Waymo found that its software had incorrectly predicted the future movements of the pickup truck due to “persistent orientation mismatch” between the towed vehicle and the one towing it. The company developed and validated a fix for its software to prevent similar incidents in the future and started deploying the update to its fleet on December 20.