I have a 98 ML320 with about 73K on it now, last week, on a cold start, no interior lights, no cranking, it sat completely dead. I reversed it out of the driveway in neutral and called MB Roadside, the tech came, and jump started it, but it would start, then stall. I brought out the spare blade key, and it fired right up. I was told the key was malfunctioning and that I needed a new battery. So after getting both replaced and normal driving for two days, this morning, again on a cold start, the car is completely dead again...no lights, nothing. I called MB Roadside again, the tech came and tried to jump it, but now it just cranks, no go with either key. He told me to tow it into the dealership, and thought the problem to be CPS or fuel pump. I don't have access to an OBDII, but I don't know if it would even work without power anyway. Any ideas of what it could be before I take it in? And expected repair costs?

 

For future reference, it was the fuel pump relay...$16 fix from the dealership