Mercedes-Benz active bonnet hood malfunction see owner's manual warning message

While not all Mercedes-benz prior to 2010 models have active bonnet feature installed as standard equipment, the models in early 2010 has got this feature as optional; making it a standard equipment in all newer vehicle models  such as S-Class W222. Purpose of designing and installing this feature in all newer models is to improve pedestrian protection while your Mercedes benz is on the road and involved in an accident, or faced an emergency braking situation, or you hit a pit or pothole on the road. Your Mercedes-benz typically displays a “active bonnet malfunction see owner’s manual” warning message on the dashboard in an event of collision to mitigate injury to pedestrians or roadrunners should you hit one.

What does active bonnet malfunction means?

active hood malfunction, see owner’s manual

When you collide on the road, with a huge bang, the rear edge of the hood near the windshield would lift up to 2 inches to ensure pedestrian safety and even if you will put it back in place, the message saying “active hood malfunction, see owner’s manual” will still appear. Active bonnet system helps to create an additional space between the hood and the engine for improved roadrunners protection and when closing the hood doesn’t disappear the display of message, we call it active bonnet malfunction. You may simply close the hood by following easy steps as mentioned in owner’s manual:

  1. Keep your hands flat and press the both sides of active bonnet at the rear where bonnet hinges are found
  2. Press down until you hear an audible click

How to reset Mercedes active hood?

If the active hood warning message was triggered and didn’t disappear after closing the hood, it is possible that the replacement of Mercedes actuator will serve the resetting purpose. But the replacement of any part should be left to the last option. A proper diagnosis of fault codes related to active bonnet actuators using a mercedes benz scanner is recommended before replacement. You can use Mercedes benz specific scanners such as

  • Foxwell for Benz,
  • iCarsoft for Mercedes, and
  • Autel Professional scanner to read and clear the fault codes.

What causes active hood malfunction?

Primarily, SRS/ Airbag module and accelerator sensors installed at the front of your Mercedes benz activates and controls the active bonnet feature.  Your Mercedes-benz driver side has a hood latch, actuator and micro switch while the passenger side has a simple latch and release mechanism. Damage caused to any part of these two controlling apparatus may result in active hood malfunctioning.  These damaged parts could be hood actuators, sensors, hood latch or SRS module itself.

Hood actuators

After an accident, the problem identified as most common is the damaged hood actuator which triggers the Active Hood Malfunctions See Owner's Manual error message. Luckily, this common problem has got a very common solution as well – Replacement.  You can replace the faulty or damaged hood actuators with the new ones and depending on the issue; you might be required to clear the codes from SRS module as well.

Acceleration Sensors

There are impact sensors behind bumper, which should be connected and working too, for active bonnet. If your Mercedes benz hood is properly closed and neither the vehicle is collided anywhere but still your dashboard is displaying a Active Hood Malfunctions See Owner's Manual message then it is possible that these two acceleration sensors residing in the bumper may be damaged or disconnected.

Hood latch

Hood latch and micro switch doesn’t contribute much to this malfunctioning but yes, If the latch gets bent or misaligned during or after an accident, it may prevent the switch from operating correctly.

SRS Module

If the hood is closed and the airbag light is on, active hood malfunction message may still appear because of following reasons:

  • the wire harness to the hood actuator,
  • the hood actuator has previously deployed
  • the airbag module has been unlocked with a professional diagnostic during diagnostics.

In all that cases, replacement of bonnet actuators and clearing fault codes from SRS module is recommended. However, you will need Mercedes benz specific scanners to further read on and clearing fault codes related to active hood system.