This blog will provide answers to the following questions: Why does the ‘stop vehicle leaving the engine running’ message come in Mercedes Benz? what are the different components used to monitor the battery? How to rectify the message and lastly, some tips to improve the battery life in your Mercedes Benz.
Why does the ‘stop vehicle leaving the engine running’ message come in Mercedes Benz?
The ‘ stop vehicle leave engine running’ message comes in Mercedes Benz cars because the state of charge of the main battery is low. The main battery in the vehicle can get discharged by keeping the ignition and standing lights ON for too long. The message appears in yellow colour which means it is not a critical fault and the vehicle can be driven once the battery gets charged from the alternator.
If the message does not go away after driving the vehicle for 10-15 min then visit the nearest authorised workshop to check the condition of the main battery and the battery sensor. All the Mercedes Benz cars have a battery sensor that is used to monitor the state of charge of the battery and prevent overcharging.
What are the key components involved in the battery monitoring function?
The battery monitoring function is programmed in the front signal acquisition and actuation control unit. the following components are used to monitor the state of charge of the battery:
- Battery sensor
It is located on the negative terminal of the main battery, the battery sensor measures the temperature and voltage level of the main battery. The sensor takes the power supply from the positive terminal of the battery.
The signal line is directly connected to the front SAM control unit, the front SAM is the master and the battery sensor communicates in LIN protocol. Xentry diagnosis tool can read the actual values of the battery sensor, it is used to determine the condition of the battery.
The data from the battery sensor is also visible in the workshop menu of the instrument cluster. It is a very important sensor in the battery monitoring system. If there is an internal fault in the battery sensor then the control unit cannot monitor the state of charge of the battery.
- Battery disconnect switch
Mercedes Benz introduced the battery disconnect switch with the launch of the E Class W213 and since then it is present on all the latest models. It is a mechanical relay that can disconnect the vehicle’s onboard electrical systems from the body.
The front SAM control unit is used to open the relay when the battery voltage goes below 11.7 volts. The electronic ignition switch closes the relay when the vehicle is unlocked.
If there is a parasitic drain or any control unit is malfunctioning, the battery disconnect switch is opened and closed 3 times in an attempt to reset the control unit. If the battery drain is still high then the switch remains open to ensure the next engine start.
- No load current relay
It is found on the old models, it is controlled by a single onboard electrical power supply control unit. No load current switch opens after 75 min is elapsed since locking the car.
The battery voltage is monitored by the onboard electrical control unit but if there is a faster parasitic battery drain, no load current relay cannot prevent the battery from getting completely discharged.
How to rectify the ‘stop vehicle, leave engine running message’?
When the vehicle shows a‘ stop vehicle leave engine running ‘ message in the multi-function display, there is a fault code logged into the front signal actuation and acquisition control unit. An authorised diagnosis scanner can run checks on the main battery of the vehicle and generate a control unit log.
A visual inspection of the battery is also performed, there should be no cracks or accidental damage to the battery housing. The battery terminals must be properly installed, if there is corrosion on the terminals then they must be cleaned or replaced accordingly.
The main battery is replaced depending on the result of the control unit log and the visual checks. Battery life on Mercedes Benz cars is usually 4-5 years but if it is a new generation car like A, B CLA and GLA then it is slightly less.
The main battery is covered under a standard warranty. There is no warranty for the Main battery if the vehicle is in 4 or 5 years unless the customer paid for it. Mercedes Benz gives a two years warranty on spare parts.
If the message still occurs after replacing the main battery, then there could be an internal fault in the battery sensor. Or open or short circuit in the electrical lines between the battery sensor and front Signal acquisition and actuation module.
Tips to improve the battery life in Mercedes Benz.
Mercedes Benz AGM or absorbent gel mat batteries in all the models, AMG batteries are more expensive than flooded batteries but they offer more stable voltage and reliability. Following are some tips to improve the battery life in Mercedes Benz
- Mercedes Benz cars can detect the presence of the drivers, therefore do not leave the ignition On for a long time. If you are waiting in the car then turn OFF the ignition, and open and close the driver’s door once. This will indicate the driver has exited the vehicle and the battery will not be drained.
- Use the hibernation mode if the vehicle is not going to be used for more than a month. In hibernation mode, the control units are disconnected from the 12 V as the battery disconnect switch is open. The hibernation menu will even indicate the number of days remaining according to the state of charge of the battery.
- Do not install non-genuine accessories in the car as they are directly connected to the main battery of the vehicle. The battery monitoring system cannot recognise the additional load since the accessory does not communicate with the CAN network.
The non-genuine accessories can slowly discharge the main battery, Mercedes Benz can even reject the warranty claims if they are installed in the car.
- Purchase a trickle charger for the car, a trickle charger can keep the main battery in good condition if the car is not used frequently or mostly kept in a garage. A trickle charger is only designed to maintain the voltage level in a battery, it cannot charge a discharged battery.
This blog explained the causes of the ‘Stop vehicle leave engine running’ message in Mercedes Benz cars. The main battery is tested with the help of a Midtronic battery tester during the scheduled service of the car, always checking the battery report and replacing the battery if the result shows the battery condition is not good.