I just picked it up, the next morning the check engine light is on, after having the vehicle inspected by Mercedes and checking it out/driving it three times before signing the deal! Fault code P0544 egr temp sensor bank 1, a google search reveals cleaning all 4 sensors in the exhaust system, is this the right way to go? I thought the senor would be on the engine somewhere with the egr valve...I have no problem pulling and inspecting them but a way to test them would be good (resistance value?). The truck has 106900 kms.
Otherwise really like the vehicle, not quite as sporty as I like my rides to be but extremely relaxing to drive and surprisingly fuel efficeint, 200km drive home resulted in 7.8L/100kms on dash readout at 105km/h. Rain and wet roads too. I am just glad I was able to find a good clean one and not resort to a minivan...!

All fixed, just removed both sensors and soaked with mass air flow cleaner and intake cleaner, blew out with compressed air and no more CEL, 5 minute fix very easy access.

I have the same problem with my R 320 CDI. Do you have any pictures showing where the EGR valve is located?