PRE-SAFE Functions Limited: What Does It Means, And What Causes It?

A PRE-SAFE Function Limited warning message indicates that the PRE-SAFE system on your Mercedes has malfunctioned. It is an in-house safety technology developed by Mercedes to reduce the severity of an accident when it happens.

The PRE-SAFE system is part of the restraint system, aiming to reduce driver and passenger injuries during an accident. In certain situations, the system can even prevent an accident. It is currently available on select Mercedes models only, as it does not come as a standard feature.

What causes the PRE-SAFE Function Limited warning message, and how does the system work? Continue reading for more details on the topic.

What Does PRE-SAFE Function Limited Warning Message Mean?

If you see the warning message “PRE-SAFE Function Limited,” it means that the PRE-SAFE system is not working properly. This could be due to a number of factors, such as a sensor malfunction or a problem with the system’s software. It usually happens when the radar sensor in front of your vehicle, just behind the bumpers, has problems. They may be dirty, blocked by debris, or damaged by moisture.

PRE-SAFE Functions Limited Mercedes

The warning message could also appear when you drive through heavy rains or snowy or dusty roads. The radar sensor could be clogged by snow or ice, hampering the operation of the Pre-Safe system.

In other words, the PRE-SAFE Function Limited warning message tells you that something is not right with the system and it needs your attention. You should diagnose the system, including checking the sensors. It is the only way to find and solve the problem.

If you see this message, it’s important to have the system checked by a qualified technician as soon as possible. Depending on the cause of the problem, the PRE-SAFE system may need to be repaired or replaced.

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What causes the PRE-SAFE Function Limited warning message?

The PRE-SAFE system is a highly technologically advanced system, relying on multiple components. Thus, there are higher chances of something going wrong in such a complex system. It can be something as simple as dusty sensors or as complicated as software malfunctions. Let’s explore a few of the most common causes of the PRE-SAFE Function Limited warning message on your Mercedes Benz.  

Software Malfunction (a software update will fix this)

The PRE-SAFE system relies on the software to respond appropriately to the input data it receives from the radar sensors. Although experts carefully coded software, eliminating all the bugs is nearly impossible. It may still fail to respond to ever-changing real-life situations.

Software glitches or bugs are one of the most common causes of PRE-SAFE Function Limited warnings. Fortunately, you can fix it by updating the system with the latest software released by Mercedes. Drive to the dealership close to you for help!

Dirty Sensors

The pre-Safe system uses a system of radar sensors mounted on the front of your car. These sensors can get dirty or blocked by debris when driving in harsh road conditions. Most drivers report that the PRE-SAFE Function Limited warning message appears on the dashboard when they go on a snowy or dusty road or when driving in heavy rain. It can be the same thing in your case. The radar might be blocked by debris, triggering the warning message.

Cleaning the sensors can help remove the snow or dirt from the sensors, causing the warning message to disappear.

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Condensation Forms Behind the Plastic and Sensors

Similar to a camera, a radar sensor will need a line of sight to operate properly. In the early morning, condensation can form behind the front bumper, hindering radar’s ability to detect the objects in front of the vehicle. The module controlling the collision avoidance features of the car will sense a malfunction with the sensors and display a warning on your instrument cluster.

The good thing is that once the condensation dries up, the warning will disappear.

Faulty Control Module

A control module is a computer that interprets the data from the radar sensors and responds by activating the actuators. These can include applying brakes, closing windows and sunroof, increasing tension in the front safety belts, etc. A faulty module cripples the operation of the PRE-SAFE system.

To check the control module, you will need a scanner and knowledge that a regular driver does not have. It is best to take your vehicle to a dealership or qualified mechanic to check the control module for possible errors. It is the only solution. Fortunately, this is rarely the cause of the PRE-SAFE Function Limited warning message.

Loose Sensors Connections

A PRE-SAFE system depends on the sensors to monitor the environment around your car. And for it to get the data needed, the sensors should always stay connected to the bus for communication. Unfortunately, connecting wires can corrode and break over time, creating an open circuit in the system.

Check the wire harness that goes to the system sensors and fix any loose connections. You can refer to the owner’s repair manual to know the location of every sensor and its connections. It is possible to fix this in your garage if you are a DIYer, but it should not cost much if you visit an auto repair shop.

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Loose Throttle Body Switch Plug

A loosened throttle body switch plug can also be the root of your problem. If the wiring harness connector plug that goes to the throttle body is not making good contact, your Mercedes will turn off the PRE-SAFE system and display a warning message.

Usually, the warning will be accompanied by other warning lights, such as the ABS or Traction Control, as these safety systems also get their data from the throttle body. It is worth checking the connections to ensure they are tight and corrosion free.

ABS and ESP System Issues

Faults with the ABS and ESP (electronic stability program) systems are likely to interrupt or limit the functions of the PRE-SAFE system. Damaged wheel speed sensors and malfunctioning ESP control units are among the most common causes.  

Use a diagnostic tool to read the stored fault code related to the ABS and ESP. Addressing these issues first may help restore the operation of the PRE-SAFE system, and the warning message will reset itself.

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What is Pre-Safe in Mercedes-Benz?

Mercedes is spending resources and time to ensure the safety of passengers in their cars is a top priority. It has developed different safety systems, including the PRE-SAFE system. This system works in two parts: it minimizes the chances of accidents occurring and reduces the severity of injuries in case of a crash. But how does it do this?

Detecting Objects and Braking

PRE-SAFE is an advanced system comprised of different radar sensors mounted behind the front bumper and the Mercedes star sign. It also incorporates the supplemental brake assist plus the PRE-SAFE brake and pedestrian detection ability.

Long, medium and short-range radars monitor the lane directly in front of the car. It ensures early detection of road users as well as other objects. The information recorded is used to determine the collision risks, allowing the system to automatically apply 40% of the braking power in an emergency. It also alerts the driver through an audio-visual alarm. If the driver responds by stepping on the foot pedal, 100% of the braking force is applied to decrease the impact upon collision. That happens even when the driver presses the brake pedal lightly.

The PRE-SAFE brake, in case of a pedestrian collision, is effective up to about 30 MPH. It can also reduce the severity by up to 45 MPH. Overall, it is a life-saving feature that should be in every car.

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Reducing Impact

The PRE-SAFE system’s first phase reduces the chances of accidents occurring. But if the crash is unavoidable, it responds by activating other safety features to minimize impact. It does a chain of actions in preparing the vehicle for an impending collision, which includes the following:

  • Adjusts the front head restraints for maximum crash protection, which reduces and prevents injuries to the vehicle occupants.
  • Rolls up the windows and sunroof to prevent debris, such as broken glasses and vehicle parts, from entering the cabin.
  • Increases tension in the front safety belts to protect passengers from injury and reduce the accident’s severity.
  • If selected, the PRE-SAFE sound mode produces a tone that makes the inner ear protect the eardrum from possible damage from any loud noises during a crash.
  • Automatically activate hazard lights when braking to warn other drivers behind you about your dangerous situation.

Which Mercedes Vehicles Have Pre-Safe System?

The PRE-SAFE system is available only in some Mercedes vehicles. It is available in the select new models, which include the following:

  • Mercedes-Benz A-Class
  • Mercedes-Benz C-Class
  • Mercedes-Benz GLC
  • Mercedes-Benz GLE
  • Mercedes-Benz GLS
  • Mercedes-Benz G-Class
  • Mercedes-Benz SL
  • Mercedes-Benz E-Class
  • Mercedes-Benz S-Class
  • Mercedes-Benz CLA
  • Mercedes-Benz CLS
  • Mercedes-Benz SLC
  • Mercedes-Benz GLA
  • Mercedes-Benz GT

Is It Safe to Drive with This Warning?

The vehicle is still safe to drive, similar to a car without any collision prevention systems. However, you should pay extra attention to the road when driving. As reliance on modern safety systems increases, some drivers start to pay less and less attention to the road in front.

The malfunctioning PRE-SAFE collision preparedness system will not compromise any other systems. The engine may still function at full power, and handling can still be on top. However, don’t ignore the PRE-SAFE Function Limited warning message. Try fixing it by cleaning the sensors or taking the car to the dealership for further diagnosis. You will likely pick up your vehicle the same day you took it there.

Is there any recall from Mercedes addressing the issue?

No. PRE-SAFE is a professionally created system that performs as intended. There has never been any recall, and any issues are treated as specific to the car. If the PRE-SAFE Function Limited warning message appears on your dashboard, take your vehicle for diagnosis and fixing. There is no cause for an alarm.

Final Remarks

The Mercedes PRE-SAFE system is a crucial safety feature on select models. It improves the safety of the driver, passengers, and pedestrians. It relies on other auto systems, such as supplemental radar systems, ABS, and sensors, to deliver as designed. Failure in any of these systems will cause a PRE-SAFE Function Limited warning message since its performance will be hampered. You should fix any problem with this system as soon as possible for safety reasons.