Hi,this fault has occurred intermittently over the last year, putting the car into limp mode, and now is very much more frequent, almost constant.
I pinned into the hi speed CAN BUS junction in the drivers footwell area and captured the trace shown below.



I then disconnected each control unit from the junction connector in turn until the trace returned to a correct CAN BUS waveform. This was when the engine ecu was disconnected.
I then pinned into the engine ECU multiplug CAN pins and with the ECU multiplug disconnected from ECU the trace was good, on re-connecting to ECU it went bad as above. This confirmed the wiring from the junction connector to the engine ECU was good and the fault is within the engine ECU itself.
Is my procedure here ok or have I missed something?
I then decided to get the ECU tested, difficult to test these apparently but used a company on the Isle of Wight (as recommended by Allcar Electronics) as they have done these in the past.
Result; nothing wrong with it.
Phoned local Mercedes parts to find that these ECU's have been superceded 8 times and 42 have been sold in the UK in the last 12 months.

I am now at the stage where I am sure it's the ECU faulty but would like confirmation that my diagnostic procedure is correct.

Thanks, Martin.