Mercedes “Active Brake Assist Functions Limited”: What It Means

By The ECU Clinic · 13 Oct 2026

Active Brake Assist is the Mercedes-Benz system that watches the road ahead and can warn you, or help brake, if a collision is likely. When the dashboard says “Active Brake Assist functions limited”, the car is telling you the system cannot work fully right now.

Common reasons for the message

• Blocked sensor. Dirt, rain, snow or a sticker over the radar sensor in the front of the car, or the camera area of the windscreen, can limit the system for a while.
• Sensor or alignment fault. A damaged or misaligned radar sensor, for example after a minor knock to the front.
• Other brake or stability faults. Active Brake Assist relies on other systems such as ESP. A fault there can also limit it.

What to check first

If the message appears in heavy rain or after the car gets dirty, clean the front of the car and the windscreen, then restart. If the message clears and stays away, it was most likely a temporary blockage.

When it needs a diagnosis

If the message stays on, keeps coming back, or appears with an ABS or ESP warning, the system has stored a fault code. Reading that code shows whether the cause is the sensor, the wiring, or a brake system unit such as the ESP module.

We diagnose brake system warnings like this one and tell you what is causing it before any part is changed. WhatsApp us a photo of the dashboard, your car model, chassis number and the fault code.