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Car Brakes By Itself (Phantom Braking)

A car that suddenly brakes or warns of a collision when there is no obstacle usually has a dirty or misaligned radar or camera, or the system has misread shadows, bridges, parked cars or reflections.

High risk

Get it checked soon. Unexpected braking can cause a rear-end collision; stay alert and keep the sensors clean.

Short answer · Why does my car brake suddenly for no reason?

Automatic emergency braking uses a radar in the front grille or bumper and a camera behind the windscreen. Dirt, snow or a stone chip in front of the sensor, or a sensor knocked out of alignment after a minor impact or windscreen change, can make it misread the road. Bridges, shadows, metal plates and cars turning off can be mistaken for obstacles. Software updates often improve this.

On this page

Safe checks you can do

  1. Clean the sensorsClean the radar area on the front and the windscreen in front of the camera.
  2. Think about recent workWindscreen replacement or a front knock may need recalibration.
  3. Note where it happensThe same bridge or junction helps the workshop.

Questions that narrow it down

  1. Was the windscreen replaced?Camera may need calibration.
  2. Was the front bumper hit?Radar may be misaligned.
  3. Are there warning messages?Sensor blocked or faulty.

Possible causes

Listed without ranking. Use the questions above to see which ones fit your car.

  1. Dirty or blocked sensorSnow, dirt or insects.
  2. Misaligned radarAfter a front impact.
  3. Camera not calibratedAfter windscreen work.
  4. Misread road featuresBridges, shadows, reflections.
  5. Software issueUpdates may help.

Questions about Car Brakes By Itself (Phantom Braking)

Can I turn off emergency braking?

Many cars allow it temporarily, but it is an important safety system.

Is calibration needed after a windscreen change?

On cars with a windscreen camera, usually yes.