📖 The Quick Answer
A forward-facing radar, camera, or both watch the road. When the system calculates that you are closing on the vehicle ahead too fast to stop, a bright warning flashes on the dash or windshield (often a red car icon) and an alarm sounds. FCW alone does not brake the car. It expects the driver to react.
⚙ How It Works (Sensors and Algorithm)
Most FCW systems share hardware with AEB and ACC: a 77 GHz forward radar plus a camera behind the windshield. The ADAS computer continuously computes time-to-collision based on closing speed and gap. The warning fires when time-to-collision drops below a tunable threshold (typically 2.5 seconds). On vehicles with AEB, FCW is the first stage and brake application is the second.
🛡 What It Protects Against
Rear-end collisions caused by distraction, fatigue, or short following distance. IIHS estimates FCW alone reduces rear-end crashes by about 27 percent, and FCW combined with AEB by about 50 percent.
⚠ Limitations and When It Fails
Same as AEB: bad weather, dirty sensors, sharp curves, and unusual obstacles. FCW also produces nuisance alerts on overhead signs, parked cars near tight curves, and animals at the road edge. Drivers sometimes silence the alert or set following distance too short and ignore it.
🚗 Which Vehicles Have It
Bundled with AEB on every new US vehicle since September 2022, and on most 2018+ vehicles before that. Branded under the same names as AEB (Honda Sensing, Toyota Safety Sense, Subaru EyeSight, Ford Co-Pilot360, etc.).
🔧 Related TSBs and Recalls
Same TSBs and recalls apply as for AEB. Several Subaru EyeSight TSBs cover false FCW alerts in low sun caused by camera glare.