Q: Car won't start. Can't determine if either ISM is bad or hydraulic valve body need to be replaced.

I presume your saying that your car does not crank when you turn the key, because that is the only fault I would expect to be associated with transmission parts controllers.The ISM (intellegent servo module) is responsible for the transmission gear position and might not allow the car to crank over if it does not recognize that the car is in park. However, if your car is cranking over, but not starting it’s possible that you’re barking up the wrong tree. Interpreting the codes that you read on the scan tool can sometimes be far more subtle than simply replacing the part that is named in the code. And replacing parts until the car works can get very expensive very quickly. For some help with your diagnosis, you can contact Your Mechanic, they can send a technician to your home or office to check out your Mercedes on the spot and recommend a repair