In my 2001 ML320. I do not know why. THis light stays on all the time. I have tried hitting the ESP button and nothing. What does BSP/ESP mean anyway??

Thank you

 

I don't know what BSP is. Did you mean ABS, BAS?
ESP is Electronic Stability System.
ABS is Anti lock braking system
BAS is brake assist system
These systems are "invisible" safety systems. Basically they ensure that the appropriate braking force is applied to stop the wheels, OR THE WHOLE CAR, from spining in an emergency or difficult situation! They are very complicated and ESP is important on 4X4 vehicles when driven at highway speeds since this type of vehicle is inherently less stable than a sedan / sports car due to it's height.
The brakes will continue to work in a BASIC (like on cars 10 years old) manner but the cause of the problem needs to be identified and corrected as soon as possible. It is this type of technology that you are buying when you buy a MB.
It is likely that you will need to take your car to a MB workshop with STAR diagnostics so that the computers that operate the systems can be interogated to assist in correcting the fault(s). Suggest you ask for a quote once the electronic diagnosis has been completed since repair can be (very) expensive.
Suggest you read your handbook. You will be surprised by what these systems do should you be in an emergency system!
Stuart