Tesla was recalling over a half a million US electric cars due to a "Boombox" feature that can drown out audible warnings for pedestrians, in the fourth recall made public in two weeks, records showed Thursday.

The automaker faces increasing scrutiny from American regulators, as watchdogs have accused Elon Musk's firm of pushing safety limits.

US authorities have set specific standards for the sounds that electric and hybrid vehicles must make, which are quieter than vehicles with internal combustion engines, in order to warn pedestrians.

Yet the "Boombox" option launched by Tesla in late 2020, which allows custom sounds like music to be emitted from an outdoor speaker when the car is parked or moving, could interfere with that warning, the National Highway Traffic Safety Administration found.

This "could increase the risk of a collision," NHTSA said in a recall report dated February 4, which notes Tesla is not aware of any accidents caused by this problem.

The regulator said about 578,600 cars were potentially involved in the recall, which Tesla plans to solve by remotely updating its software rather than forcing owners to come to service centers.

The agency sent an initial request for information to Tesla about "Boombox" back in January 2021 and then held several meetings with the manufacturer, which tried to defend the compliance of this option.

Tesla vehicles are subject to their 4th recall made public in an matter of weeks
Tesla vehicles are subject to their 4th recall made public in an matter of weeks AFP / David GANNON

But Tesla eventually agreed to disable the feature when the vehicle is in drive, reverse or neutral mode.

The "Boombox" recall is the fourth for Tesla made public in the United States in a matter of weeks.

NHTSA announced on February 1 the recall of nearly 54,000 vehicles to end a drive-assist feature that allows Tesla cars in certain conditions to go through a stop sign without fully stopping.

Two days later it announced a recall of 817,143 vehicles to adjust the seatbelt warning system, which may not activate under certain conditions.

And on Wednesday, the agency announced a recall of 26,681 cars to correct a software error related to a valve in the heat pump that can affect the ability to defrost the windshield.

Tesla has long regularly performed remote software updates without necessarily notifying users or regulators.

But NHTSA has stepped up its actions against the company in recent months, including launching an investigation last summer after several crashes with emergency vehicles and requesting more information from the company.