Mercedes Active Bonnet Sensor (Here Is How It Work)

mercedes active bonnet sensor

Mercedes-Benz has always been a pioneer in the automotive industry, continuously pushing the boundaries of innovation and safety.

One of the latest advancements in Mercedes-Benz vehicles is the integration of an active bonnet sensor, a feature designed to improve pedestrian safety in the event of a collision.

This article delves into the details of the active bonnet sensor, its purpose, functionality, and common issues, as well as providing guidance on resetting and diagnosing potential problems.

What is an Active Bonnet Sensor?

The active bonnet sensor is a safety feature incorporated into many modern Mercedes-Benz vehicles. This system, also known as the active hood in the United States, is designed to minimize pedestrian injuries in the event of an accident.

When the sensor detects a collision, it triggers the rear edge of the hood to lift up by approximately 5 cm (2 inches) near the windshield. This creates additional space between the hood and the engine, providing a cushioning effect to help protect pedestrians from severe injuries.

Active Bonnet Sensor: Standard and Optional Equipment

While not all Mercedes-Benz models are equipped with an active bonnet sensor as standard, it has become increasingly popular in newer models.

Initially introduced as an optional feature in early 2010 models such as the R172 SLK, the active bonnet sensor has since become standard equipment in models like the S-Class W222.

Read also >> Active Bonnet Malfunction: Solved! (Step by Step)

How Does the Active Bonnet Sensor Work?

The active bonnet sensor system is primarily controlled by the SRS (Supplemental Restraint System) or airbag module and accelerator sensors located at the front of the vehicle.

In the event of a collision, these sensors relay information to the SRS module, which then activates the hood actuator mechanism on the driver’s side.

This lifts the rear edge of the hood, providing additional space between the hood and the engine for improved pedestrian protection.

Components of the Active Bonnet System

The active bonnet system comprises several components, including:

  1. Hood Actuator: The hood actuator is responsible for lifting the rear edge of the hood when triggered by the SRS module. This component is usually found on the driver’s side and includes a hood latch, actuator, and microswitch.
  2. Acceleration Sensors: Located in the bumper and cross member, these sensors detect impacts and relay information to the SRS module to activate the active bonnet system.
  3. Hood Latch: The hood latch secures the hood in place and incorporates a built-in switch. Although hood latch issues are rare, a bent or misaligned latch can prevent the switch from operating correctly, causing the active bonnet system to malfunction.
  4. SRS Module: The SRS module is the primary controller of the active bonnet system, receiving information from the acceleration sensors and activating the hood actuator as needed.

Common Causes of Active Bonnet Malfunction

Several factors can contribute to an active bonnet system malfunction, including:

  1. Damaged Hood Actuator: A damaged or deployed hood actuator is the most common cause of an Active Hood Malfunction error message. In such cases, the hood actuator must be replaced, and fault codes cleared from the SRS module.
  2. Faulty Acceleration Sensors: Disconnected or damaged acceleration sensors can trigger the Active Hood Malfunction error message, even when the hood is closed properly and the vehicle has not been involved in an accident.
  3. Misaligned Hood Latch: A bent or misaligned hood latch can prevent the built-in switch from operating correctly, leading to an active bonnet system malfunction.
  4. SRS Module Issues: If the airbag light is on, the active hood warning message may appear on the dashboard, even with the hood closed. This can be due to issues with the wire harness to the hood actuator, previous deployment of the hood actuator, or unlocking of the airbag module during diagnostics.

Resetting the Active Bonnet System

If the active bonnet system has been triggered and the hood has been lifted, it’s essential to reset the system by following these steps:

  1. Pull the hood release and open the hood.
  2. Push up on the front of the hood until the hinges click, indicating they have been pushed down into place.
  3. Close the hood.

In some cases, the active hood warning message may persist even after resetting the system. If this occurs, it may be necessary to replace the hood actuators and clear fault codes from the SRS module using a Mercedes-Benz scanner, such as the YOUCANIC Full System Scanner.

Diagnosing Active Bonnet System Issues

Before replacing any components of the active bonnet system, it’s crucial to diagnose the issue using a Mercedes-Benz scanner.

This will help identify any fault codes related to the active bonnet system and determine the appropriate course of action. Some recommended scanners include:

  • Foxwell for Benz
  • iCarsoft for Mercedes
  • Autel Professional Scanner

By reading and clearing fault codes from the SRS module, you can ensure that pedestrian protection is restored and the active bonnet system is functioning correctly.

How do you turn off the sensor on a Mercedes?

If you are looking to turn off the parking sensors on your Mercedes, it is not recommended to disable them unless it’s necessary.

The parking sensors may be fused as part of the larger vehicle system, so it may not be practical to remove them.

Calibration may also be necessary for accurate sensor performance, requiring high-end hardware and software.

Can I drive with bonnet open?

It is not recommended to drive with the bonnet or hood open, even though it is not technically illegal in most states.

The hood plays an important role in pedestrian safety and can cause vehicle damage if left open while driving. Therefore, it is best to keep the hood securely fastened to the body of the car.

What is the purpose of the active hood hinges?

The active hood hinges, also known as the active bonnet system, are designed to lift the hood’s rear edge when involved in an accident or collision with a pedestrian.

This creates space between the hood and the engine and helps to cushion pedestrians, minimizing the risk of injury. However, it’s important to note that driving with the bonnet open is not recommended due to safety concerns and potential vehicle damage.

What type of collision sensors are used in active hood hinge applications?

Active hood hinges in vehicles use fiber optic cables or deceleration sensors to detect collisions with pedestrians.

Bumper-installed pedestrian crash sensors and acceleration sensors are used by the active hood system to detect vehicle-pedestrian collisions.

When the fiber optic cable is bent or the sensors detect a collision, the electronics in the car trigger the bonnet hinges to rise and lift the hood’s rear edge to minimize injury to the pedestrian.

What is the black thing on bonnet?

The black thing on the bonnet of a car could be a car bra, which is mainly used to protect the car’s paint from stones and salt.

However, if you’re asking about the purpose of the hood hinges, they are designed to lift the hood’s rear edge in the event of a collision with a pedestrian, minimizing the risk of injury.

Fiber optic cables or deceleration sensors are used to detect collisions, and the electronics in the car trigger the bonnet hinges to rise when a collision is detected.

Mercedes Active Bonnet Malfunction (active hood malfunction) >> Check out the video below:

In Conclusion

The active bonnet sensor is an innovative safety feature that has become increasingly standard in Mercedes-Benz vehicles.

By understanding the system’s components, common issues, and the procedures for resetting and diagnosing problems, you can ensure that your vehicle remains both safe and reliable.

As always, consult your vehicle owner’s manual or a qualified professional for further guidance and assistance.

Steve P.

Steve is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Riviera. Steve is based in Boise, Idaho.

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