Active Bonnet Malfunction Mercedes: How to Fix It

The Active Bonnet System (also known as the Active Hood) is part of the pedestrian protection system in your Mercedes. When a malfunction occurs, the system cannot properly deploy the bonnet in the event of a collision. Here's how to address the issue:

Step-by-Step Troubleshooting and Fix

1. Active Bonnet Malfunction Mercedes: Check for Obvious Issues:

   • Make sure the bonnet is properly closed.

   • Visually inspect the bonnet hinges — if the rear of the hood looks raised, it may have been deployed.

   • Look for signs of previous minor collisions.

2. Scan for Fault Codes:

   • Use a Mercedes-specific diagnostic tool such as Xentry, MB Star, or iCarsoft MBII.

   • Scan for DTCs (Diagnostic Trouble Codes) related to:

     • Bonnet actuators

     • Pedestrian protection sensors

     • Control modules

3. Reset or Replace Faulty Components:

   • If the system was deployed (even slightly), the bonnet actuators (lifters) may need replacement or reset.

   • Replace any faulty impact sensors or wiring connections.

   • If the control unit is faulty, a new one may be required and must be programmed using dealer software.

4. Check Fuses and Electrical Connections:

   • Inspect relevant fuses in the fuse box for the Active Bonnet System.

   • Check wiring harnesses for corrosion or loose connectors.

5. Software Reset:

   • After repairing the hardware, use the diagnostic tool to clear the error codes.

   • Perform a system test to ensure all sensors and actuators respond correctly.

Important Notes:

• If the Active Bonnet was deployed during a minor collision, it must be reset or replaced before the warning will go away.

• Driving with this system malfunctioning does not affect normal performance, but reduces pedestrian safety, especially in accidents.

• Only trained technicians or authorized Mercedes-Benz service centers should attempt full system repairs or reprogramming.

Let me know your exact model and year (e.g., E300 2019), and I can give you more specific repair instructions or part numbers.