Mercedes Collision Prevention Assist Plus Inoperative Message

You are driving down the highway and suddenly your Mercedes-Benz displays a warning message "Collision Prevention Assist Plus Inoperative See Owners Manual". 

Throttle response becomes very sluggish and the car feels like it has no power.

Mercedes Collision Prevention Assist Plus Inoperative See Owners Manual
Mercedes Collision Prevention Assist Plus Inoperative Message

This is a problem reported by many 2015 and newer Mercedes-Benz C-Class, GLS-Class, E-Class owners.

Collision assists malfunctions can be caused by something as simple as low battery voltage but can also be an indication of a faulty Engine Control Unit (ECU).

What does Collision Prevention Assist Plus Inoperative mean? 

Error message Mercedes Collision Prevention Assist Plus Inoperative See Owners Manual means that the system has malfunctioned.

COLLISION PREVENTION ASSIST PLUS monitors the traffic in front of the vehicle. If it determines that you are about to hit another car it will warn you with a message on the dashboard plus an audible sound. 

With collision assist disabled your vehicle will no longer avoid a potential accident or automatically apply the brakes if you get too close to the vehicle in front of you. 

Keep a safe distance from the vehicles in front of you and stay alert.

If the waring happened only one time and went away after restarting the vehicle, there may not be a reason to worry. 


In most cases, you will experience one or two of these symptoms: 

  • Collision Prevention Assist Plus Inoperative message
  • Vehicle loses power or won't respond to the gas pedal
  • Transmission gets stuck in limp mode
  • Car won't acceleration
  • Brake Assist warning message on dashboard

Common Causes

  • Low temperatures:  Extremely low or high outside temperatures can affect the system and cause it to malfunction 
  • Interference: You may get Collision Prevention Assist Plus Inoperative error if you are driving near sources of electromagnetic radiation such as driving near a radio station. 
  • Battery Voltage: This message may come up if the battery voltage is too low. For example, if you turn off the engine but keep the ignition on while parked. Once you restart the car, you may be greeted with Collision Prevention Assist Plus Inoperative error message. Keep the vehicle running at idle or driving for about 30 minutes should charge the battery and reset this warning. 
  • Sensors: Sensors mounted at the front of the vehicle may stop working correctly if excessive dirt is at the front of the car. 
  • Engine Control Unit Pins: Poor Engine Control Unit (ECU)  connections due to loose, dirty or overspray pins can cause communication issues with the accelerator pedal (gas pedal), proximity sensors,  throttle actuator contacts. This may be the problem if a vehicle is scanned with Mercedes STAR scanner and fault codes are stored for implausible data or communication.  

What to do?

While getting this error once a year may not be a concern, you want to get the system diagnosed if the Collision Prevention Assist Plus Inoperative error keeps coming up periodically. 

Restart Vehicle

Restart vehicle to reset Mercedes Collision Prevention Assist Plus Inoperative See Owners Manual

Find a safe location. Pull over, turn off the ignition, wait 2 minutes and restart the vehicle.

If the battery is partially discharged, you may need to let the car idle for at least 15 minutes before the error can be reset. 

Distance Sensors 

radar sensors Mercedes Collision Prevention Assist Plus Inoperative See Owners Manual

Inspect the front bumper for excessive dirt or ice.

Clean the bumper by removing any dirt that may be on the bumper or on the cross member that is mounted near the radiator. 

Update Software

Ask the dealer to perform a software update for the Collision Prevention Assist Module.

Locate a Mercedes-Benz dealer near you. Call them and provide your VIN.

The dealer can tell you if there is a software update available that may fix your Collision Prevention Assist Plus Inoperative problems. 

If your dealer is not able to help consider filing a complaint with the National Highway Trafic Safety Administration (NHTSA). 

Diagnose Collision Assist Modlue 

To diagnose this problem further you will need a scanner that can read and clear Mercedes-Benz specific fault codes. 

Diagnostic scanners that work on Mercedes-Benz include iCarsoft MB II, Foxwell for Benz, Autel MaxiDAS full system scanner

By YOUCANIC on Jun 26, 2019


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