Some recently manufactured Tesla models have had their automatic emergency braking (AEB) systems turned off while the automaker examines real-world data to ensure that the system will work as intended, a spokeswoman said Sunday.

The system should be available to owners within 6 weeks, Tesla said, even though the vehicles were initially sold as having AEB as standard equipment.

This update applies only to Tesla vehicles built since Model 3 production began in late July, including all Model 3s, as well as newer Model S sedans and Model X SUVs. That means it will not affect the AEB systems on the vast majority of Teslas on the road today. CR learned about this move from a note posted by a Tesla owner on a Reddit message board; that owner said he received his notice on Saturday.

According to a Tesla statement from early August, the company updated some of the hardware for new vehicles across its line. “This hardware set has some added computing and wiring redundancy, which very slightly improves reliability,” the company said.

That update apparently led to Tesla’s move to evaluate its AEB system in these new models. "We recently introduced some minor hardware changes to the Autopilot system in new cars, and we are now in the process of robustly validating the new hardware using real-world driving data,” a Tesla spokeswoman said in a statement Sunday afternoon. “During that process, Automatic Emergency Braking will temporarily be inactive and will instead be in shadow mode, which means it will register how the feature would perform if it were activated, without taking any action. This temporary calibration period is standard Tesla protocol and is done out of an abundance of caution.”

While the AEB system of these Teslas is in shadow mode, the early collision warning systems and all other Autopilot features of the vehicles will still be active and functional, Tesla said.

One of the unique features of Tesla vehicles is that they receive over-the-air upgrades automatically, says Jake Fisher, Consumer Reports director of auto testing. "Tesla can deliver cars prior to fully developing the software needed for new features, with plans to update the cars later,” he said.

Over-the-air updates open many possibilities. Tesla this week provided owners living in the path of Hurricane Irma whose vehicles have a 60kWh battery a temporary, free over-the-air upgrade to give those vehicles more range in case owners wanted to evacuate. That was possible because Tesla models sold as 60 kWh actually have the capability to be 75 kWh vehicles; normally, the owner would have to pay to expand that battery pack.

“The downside for Tesla owners,” Fisher said, “comes when promised features are delayed. Owners who paid for those missing features have little to no recourse."

That happened to buyers of Tesla Model S and Model X vehicles built after Oct. 2016. Although those owners were promised AEB would be a standard feature when they bought their new Tesla, it took until July 2017 for the software to be updated that made it fully functional. In fact, on the Tesla website Sunday, AEB is still referred to as a standard safety feature for all new Model S, Model X and Model 3 versions.