I ran into a problem yesterday, both the windscreen and headlight pumps stopped working at the same time.

I've checked for leaks but there are none that I can find. So I took a look at the connectors and all seems well. The weird thing is that when I setup for the voltage check I found to my amazement that the pump was getting 12v even when the car is turned off, I would have expected it to be 0v.

I'm starting to think it might be the SAM thats gone nuts as both pumps are effected.

Should I head to the stealership or does anyone have any ideas?

 

I would try unplugging the negative battery cable, and then waiting about 15 minutes. Replug it and see if that fixes your problem. Sounds like some random electric fault that should be solved with a complete power down of the system.

 

It is easier for a transistor to pull a positive voltage to ground than supply a positive voltage to a circuit. +12 is always sourced to the pump motor on the "high" side. The "low" side of the motor is connected to the SAM. When instructed via the CANbus, the SAM turns on the transistor and connects the low side of the motor to ground. The motor runs as long as commanded.

Sure the SAM could be bad, but more likely is trouble on the CANbus telling it what to do, or a bad switch on the steering wheel stalk, or the headlight module (where the lamp washer switch lives.) It can also be a dodgy connector on the steering wheel clockspring (Mercedes for "slipring")

You could also have a problem with the wiring under the hood. The wire from the motor low side might not have continuity with the SAM. A check of the terminal in the SAM should have the same voltage (+12) as the high side of the motor when turned off.

To make sure the motor works, unplug it and briefly touch the terminals to a 12 volt source (like jumpers from the battery) to make sure the motors did not suffer damage during the winter frost season.