Collision Prevention Assist Plus Inoperative On Mercedes: Meaning & Possible Causes

New Mercedes Benz models are technologically advanced automobiles equipped with many complex safety systems. One of them is the collision prevention assist plus. It is a system of radar that monitors the distance between your car and the car in front.

Collision Prevention Assist Plus system will warn you if you get dangerously close to the vehicle in front of you. However, many drivers have reported faults with this system. When it has a defect, the warning message Collision Prevention Assist Plus Inoperable appears on the instrument cluster.

But what causes this error message, and how can you fix it? This article focuses on answering these questions and more. Read on for detailed information.

What Does Collision Prevention Assist Plus Inoperative Mean on Mercedes?

The Collision Prevention Assist Plus is a safety system in your Mercedes car. It uses a radar mounted on your car to detect any vehicle in front of you and warns you if you are getting dangerously close. This system detects small gaps between objects and vehicles in front of your car.

So, how does it function?

Collision Prevention Assist Plus is an intelligent system. It compares your speed to other drivers while on the road. It uses radar technology to determine if the collision is imminent. It will then warn you and apply brakes automatically to help avoid the accident. It can also detect rear-end collisions or impacts and alerts the driver visually or audibly.

However, if the system cannot function, you get the Collision Prevention Assist Plus Inoperable warning on the instrument cluster. That means it won’t sound the alarm to warn you of any imminent collision. That compromises your safety on the road.

The collision avoidance system has become standard in most cars, including Mercedes and select BMW, Hyundai, Honda, and Toyota.

Collision Prevention Assist Plus Inoperative means there is a fault in the system, and it has ceased working. It will not detect objects or respond to any situation and won’t apply the brakes in an emergency. It would be best if you address it as soon as possible to enhance your safety and that of other road users.

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What Is Causing the Collision Prevention Assist Plus Inoperable Warning Message?

The problem with this collision avoidance system is primarily electrical. It can be sensors, wiring, control module, and others. Let’s explore a few possible causes of this fault message and how to fix them. But before that, you can get your service manual that outlines the steps to follow when diagnosing this problem.

01. Low Battery

Your car battery can drain if the car has been off for a long time. Also, with time, the battery cells wear off and eventually die, unable to take in electrical charge, and will not support most electrical systems. That is the likely problem when the Collision Prevention Assist Plus Inoperable appears when you start the car. A weak battery interferes with the operation of radar sensors that the collision avoidance system relies on.

The warning message caused by low battery power should go away on its own after driving for a few minutes. Alternatively, you can leave the car idling for about 20 minutes to recharge the battery. But if the battery is dead, the error message will stay on the instrument cluster. It will be the case if the engine fails to crank. You may need to test the battery or recharge the battery externally.

Recharging or replacing a dead battery can help resolve the issue. But if that does not work, look for other possible causes.

02. Extreme Temperatures

High temperatures can interfere with the operation of the radar sensors used by the collision avoidance system. They may transmit out-of-range data to the control module, which detects that as a fault in the sensors and displays the warning message on the dashboard.

If the Collision Prevention Assist Plus Inoperable warning is caused by high temperatures, it should go away. It is temporary and will clear itself once the correct operating temperature is restored. But if it persists, diagnose the vehicle further to find the root cause.

03. Condensation Forms Behind the Plastic and Sensors

Radar sensors are like cameras; they need a line of sight to operate. Condensation can obstruct them, hindering their ability to detect objects in front of the vehicle. The collision avoidance control module interprets that as a malfunctioning sensor and triggers the warning message.

Fortunately, the error message goes away once the condensation dries up and clears the sensor. So, driving around for a few more minutes should help resolve the problem.

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04. Faulty Parking Sensors

The collision avoidance system in Mercedes cars also depends on the parking sensors to better detect objects, especially at the vehicle’s rear end. If these are faulty, the system becomes inactive, and the warning message appears on the instrument cluster.

You need an OBD2 scanner to read the fault code and fix faulty parking sensors if they are at fault. Alternatively, you can take the car to the dealership if you don’t have the auto diagnostic tool for scanning the fault code.  

05. Sensors Had Lost Its Data Connection with The Main Data Bus

The radar sensors used by the Collision Prevention Assist Plus should be able to communicate constantly with the control module in the system. But they can often lose communication due to software glitches or connection problems.

Inspect the wires connecting the various components of this system and fix any identified problems. If that doesn’t help, take the car to the dealership. They will likely update the software, which can solve the glitches and bugs in the system.

06. Front Camera Obstructed

Mercedes car collision systems use cameras to detect objects, similar to the Audi Pre-Sense System. But these cameras, mounted at the top of your windscreen, can be obstructed by mud or dust. That can cause the Collision Prevention Assist Plus to malfunction.

This is the most straightforward problem to fix. Clean the areas in front of the cameras, removing any dust, mud, or debris on the surface. That should restore the system, and the warning message will disappear from the instrument cluster.

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07. Poor Engine Control Unit Connection

Another unlikely cause of the Collision Prevention Assist Plus Inoperative message on Mercedes is the poor control engine unit (ECU). That can happen due to loose connections, dirt, or overspray pins that disrupt communication with sensors and actuators. The communication problem often occurs with the accelerator pedal, proximity sensors, and throttle body contacts.

Scan the vehicle with an OBD2 diagnostic tool to read the fault code that will pinpoint the cause, likely telling you about the implausible data or communication. Fixing connections to the ECU should restore the system.   

Symptoms Collision Prevention Assist Plus Inoperative Warning Message

Stay alert when on the road. Apart from just looking at the road straight ahead, you should be aware of your surroundings, which includes how your car responds. You will notice the warning message on the screen. Still, your Mercedes will also show some symptoms when the collision avoidance system fails.

Most drivers have reported the following symptoms when the Collision Prevention Assist Plus Inoperable warning comes on:

• Lose the ability to accelerate, or the vehicle won’t respond when you step on the gas pedal
• The car won’t switch gears
• Brake assist warning on the instrument cluster
• Limp mode activated

Can I drive with this error on my dashboard?

The vehicle may still drive as usual without any noticeable problems. It depends on what caused the problem, but the manufacturer advises drivers to fix it immediately for safety reasons.

Check your dashboard for any accompanying warning lights, such as the brake assist warning that may tell you how bad the situation is. Sometimes, the car switches to limp mode, not allowing you to drive to a nearby dealership or auto repair shop without needing breakdown services.

Regardless, always fix the Collision Prevention Assist Plus Inoperative error message as soon as possible. It is an important safety system in your car that keeps you safe on the road.

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How do I turn off the Mercedes Collision Warning?

Collision Prevention Assist Plus is a crucial system that should always stay on. It enhances your safety and is not worth deactivating this system. However, you may turn it off due to false positives that can sometimes become annoying.

Deactivate the Mercedes collision warning using the steering wheel and navigation buttons. Click the home button and scroll down to assistance; you will see the collision assist plus. You can choose to disable it entirely or lower the sensitivity level, which reduces the number of warning messages you get on the instrument cluster. It is also possible to reactivate it if you want it back on.

Collision Prevention Assist Plus Sensor Location

Collision Prevention Assist Plus relies on multiple sensors and cameras to keep you safe. The location of the sensors will depend on the model and manufacturing year, but they are usually located behind your front bumper.

The cameras that help the system are usually placed at the top of your windscreen, inside the vehicle, behind your rearview mirror. For a better idea, check out the diagram below.

Is there any recall from Mercedes addressing the issue?

There has never been a recall from Mercedes on the Collision Prevention Assist Plus Inoperative issue. If your system fails, it can be due to the reasons mentioned. It will be a specific issue that does not necessitate a recall. But feel free to visit the dealership in your area and ask for help if your car displays this error message.

In Summary

Automotive manufacturers equip their cars with more and more safety systems, aiming to keep you, the driver, safe and prevent any crashes. However, sometimes, these systems start to fail due to wear and tear, as well as other sorts of malfunctions.

The Collision Prevention Assist Plus from Mercedes makes no exception. While being a great system, its reliance on multiple sensors, cameras, and multiple modules, makes it prone to failing. This is when you get the warning message discussed in the article.

While not always easy or cheap to fix, and while you might still be able to drive the vehicle, fixing this malfunction is always recommended. Depending on what has caused the malfunction, the repair cost can range from $0 to $300 if you need a specialist to investigate the problem.