Why your car's automatic braking goes off when nothing is there

Your car is usually not broken. In most reported cases of so called phantom braking, the forward radar or camera has correctly detected something real and then wrongly judged it to be an obstacle in your path. A steel plate over a trench, a bridge expansion joint, an overhead gantry, a truck parked half on the shoulder, a two-wheeler cutting across a gap. The sensor reports an object, the decision software scores it as a collision threat, and the brakes do what they are told. Engineers call that a false positive, and it is the central problem in tuning any automatic emergency braking system.

Why a sensor sees a threat that is not there

Automotive millimetre wave radar is very good at two things, measuring how far away something is and how fast the gap is closing. Many of these radars have little or no elevation resolution, so they cannot reliably tell you whether a strong reflection is at road level, at bumper height or five metres overhead. A manhole cover, a drain grating and a stopped lorry can all look like a bright stationary return in your lane. The camera is there to classify what the radar found, which is why the two are fused, but a camera struggles in glare, heavy rain, a dust haze or the mouth of a tunnel.

That creates a trade-off with no free lunch. Make the system quicker to brake for a genuinely stopped vehicle and you get more nuisance events. Damp the nuisance events and the system intervenes later in a real emergency. Carmakers shift that balance with software, which is why the problem can shrink after an update. When America's NHTSA closed its four-year investigation into unexpected braking on about 695,000 Tesla Model 3 and Model Y cars on 2 July 2026, it noted that reports had fallen from 300 when the probe opened to 45 in 2024, 19 in 2025 and three so far in 2026, after Tesla pushed software updates in early 2022.

Regulators have started testing for it

False braking is now written into law in the United States. FMVSS 127, which applies to vehicles built on or after 1 September 2029, includes two false activation tests alongside the crash avoidance ones. In the first, the car is driven at 80 km/h over a stationary ASTM A36 steel trench plate measuring 2.4 m by 3.7 m by 25 mm. In the second, it is driven at 80 km/h between two parked vehicle test devices set 4.5 m apart at their closest front wheels. In both, the car must not add more than 0.25 g of deceleration beyond what the driver's own braking would produce.

The matching engineering standard is ISO 21448, the safety of the intended functionality standard, which deals with hazards that appear even when nothing has failed. Mobileye said on 22 October 2026 that TÜV SÜD had audited its automatic emergency braking development process against it.

What this means for Indian owners

India has no false activation test of its own yet, so cars sold here run calibrations developed largely for European and American homologation and road furniture. Owners notice. A CMR India survey published on 12 May 2026 found ADAS-equipped car sales up 49 per cent year on year, with 91 per cent of those cars offering Level 2 and 4 per cent Level 2 plus, yet only 15 per cent of more than 1,000 respondents were willing to pay extra for it.

Localisation is under way. Mobileye's India and China vice president Elie Luskin told Autocar Professional the company is working with carmakers to make ADAS usable here and that its Road Experience Management map data collection is already running in India.

Three practical things. Use the sensitivity or warning distance setting if your car has one rather than switching emergency braking off. Keep the windscreen patch in front of the camera and the radar area of the bumper clean and undamaged. And after a windscreen replacement or bumper repair, insist on a proper sensor recalibration, which AAA notes needs specific tools, training and information to get right.

Sources