I have a 2007 E320 CDI 3.0 estate. I'm getting a dash message 'ESP system inoperable' regularly and there is a clonk at the gearbox which then doesn't change properly. If I switch the ignition off and on a few times it eventually works ok again, but that could be for 2 minutes or 2 days ! a friend plugged my car into diagnostics and came up with this message 'ETC Electronic fault 13, No CAN message was recived from control unit transmission control module'. Does anyone have experience of what is likely to be causing this, and therefore the fix required please ? I'm hoping this isn't an expensive fix because things are tight at the moment, but I fear it could be.