I am writing this letter in regards to the 2010 Mercedes Benz S 400 Hybrid vehicle. My mother is the owner of this vehicle which has recently become a very hazardous problem for us. She was involved in two automotive accidents within the same week due to the vehicle's failure in allowing her to brake properly. Both of these accidents have resulted in both moderate to severe damage to all parties.
The problem stems from Benz's design flaw in their Regenerative Braking System (RBS). According to the owner's manual, it states that
"RBS must be activated when the vehicle is parked each time before driving off".
To activate the RBS the following instructions are given as follows:
? Make sure the automatic transmission is in park position P.
? Switch on the ignition.
? Apply the brake pedal fully and release it. The RBS is activated.
The issue with this process is that it says to fully apply the brake and release it in order to activate the RBS, but there is no actual indication for the driver to know whether or not the RBS has been successfully activated or not. Also it is stated that the brake pedal must be applied fully and then released. This notion is very subjective in a real life situation due to the fact that the average driver may or may not be aware of the level in which they are applying the brake each time they attempt to activate the RBS. For example if the driver is in a hurry or is of shorter height, he or she may believe that they are applying the brake fully when it actuality it is only 80% and as a result fails to activate the RBS. If Mercedes states that the RBS must be activated each time before driving then it should be imperative for the driver to know if and when the RBS is activated.
The reason why this issue is of such concern is due to the following instruction in the owner manual stating:
"While you activate the RBS, less brake pedal pressure than usual is required and the brake pedal travel is longer. When you release the brake pedal, the brake pedal travel is as usual again."
Now it is basically stating that before activating the RBS there is less brake pedal pressure and the pedal travel is longer than usual, meaning that if the RBS is not activated it is safe to assume that the status quo will remain and that there will still be less brake pedal pressure being required while the brake pedal remains longer. This is of major concern due to the fact if and when the RBS is not activated and the vehicle is driven in a normal fashion, the braking ability of the driver is then negatively altered. When the driver is then faced with a scenario in which they are required to come to a complete stop very quickly, the brake pedal travel being longer, alone greatly aids in the inability to do so. This then ultimately results in a collision given in any scenario.
This RBS is a technology that is utilized not only in the S400's braking system but in other hybrid vehicles as well such as the Toyota Prius and BMW ActiveHybrid 7 Series. But the design flaw in question does not stem from the RBS technology itself. It is Mercedes-Benz's implementation of an activation process that allows for slightest of human error to have great consequences when operating the vehicle on the road.
We are grateful that these accidents that my mother was involved in resulted in no severe injuries or even deaths because when dealing with a vehicle with a brake problem such as the S400, it is quite easy to do so. And depending on the driver's ability to given the parameters it takes to activate the RBS every single time before the vehicle is driven makes this vehicle a highly potential ticking time bomb.
This is simply a letter of concern for the 2010 Mercedes-Benz S400 Hybrid and would like to inform the public of this dire issue to try and further prevent such catastrophes.

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