Mercedes-Benz Active Hood Bonnet Malfunction See Owner's Manual

Mercedes-Benz vehicles may display a warning message on the dashboard that says: 

  • Active Bonnet Malfunction See Owner's Manual - UK, Europe
  • Active Hood Malfunctions See Owner's Manual - USA
 Mercedes-Benz Active Hood Bonnet Malfunction See Owner's Manual

You typically get this error message when:

  • are involved in a minor accident
  • during an emergency braking situation where the auto brake is engaged
  • hit a pothole or pit on the road

The hood will usually pop up 5 cm (2 inches)  at the back near the windshield. 

While not all Mercedes-Benz models have an active bonnet feature installed, it is becoming standard equipment on newer models.

This feature was initially available as an option on the early 2010 models such as R172 SLK but is become standard equipment on models such as S-Class W222. 

What is active hood / bonnet?  

The active bonnet system minimizes pedestrian injuries by lifting the rear edge of the hood when you are involved in an accident. 

Raising the hood creates additional space that can serve as a cushion between the hood and the engine. Active bonnet improves pedestrian protection. 

How to reset Mercedes active hood? 

mercedes active bonnet reset

If your hood pops up at the back follow these steps to close the hood. 

  1. Pull the hood release and open the hood.
  2. Keep your hands at the front of the hood and push up until the hinges get pushed down and click.  
  3. Close the hood. 

If the active hood warning message was triggered, you may need to replace your Mercedes hood actuators. Get your Mercedes-Benz diagnosed before you replace any parts. 

In some cases, you may need to use a Mercedes-Benz scanner such as iCarsoft MBII, Foxwell for Benz or Autel MaxiDAS scanner to clear the fault codes from the SRS module.

Once the codes are cleared,  pedestrian protection will be restored as well.

Common Causes

Active bonnet feature is activated and controlled primary the SRS / Airbag module and accelerator sensors installed at the front of the vehicle.

Hood Actuator

mercedes hood actuator

The most common problem that triggers Active Hood Malfunctions See Owner's Manual error message is the hood actuator that either is damaged or deployed after an accident. 

The passenger side has a simple latch and release mechanism.

The driver side has a hood latch, actuator, and microswitch.

Replacing a Mercedes-Benz hood actuator is an easy procedure. You will need to a couple of screws to replace it. Depending on the issue, you may need to clear the codes from the SRS module as well. 

Sensors

Two acceleration sensors in the bumper and one in the cross member may be damaged or disconnected. 

Any of these acceleration sensors may the culprit if you are getting the error message Active Hood Malfunctions See Owner's Manual and the hood is closed properly or you were never involved in an accident. 

Hood Latch

Active Bonnet Malfunction error message | Mercedes-Benz Owners

The latch that secures the hood and prevents it from opening has a built-in switch. If the latch gets bent or misaligned, for example, from an accident, it may prevent the switch from operating correctly. 

The hood or latch switch is rarely the culprit for the Active Hood Malfunctions See Owner's Manual warning message. 

SRS Module

mercedes slk active bonnet malfunction

If the airbag light is on, you may get an active hood warning message on the dashboard even though the hood is closed. 

The issue could be because of:

  • 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. 

Ignited hood bonnet actuators will need to be replaced and fault codes cleared from the SRS module. 

Further diagnostics

If the airbag light is on and you are getting Active Hood Malfunctions See Owner's Manual error message we recommend that you start by reading the fault codes from the SRS module. 

You will need a scanner such as Star Diagnostic or if that is not available use a Mercedes-Benz specific scanner such as:

Pay attention to fault codes related to Active Bonnet actuators.

 

Additional Resources

  1. Mercedes Active Bonet 500sec.com
  2. Pedestrian protection offered by the new E-Class daimler.com

By YOUCANIC on Jun 19, 2019

Vehicle

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