My Smart for 2 Cdi came up with an EGR fault. I found this strange because I had blanked off the exhaust supply to the EGR valve several years ago. It turned out my blanking piece, which was made out of a Nivea tin, had a hole in it and the EGR valve was totally coked up with soot and oily gunge. The valve was stuck partly open.
Disconnected the EGR valve and opened it out. Had it soaking it diesel for a few hours with actuator disconnected. I found only lots of elbow grease could shift the coke and gunge. Removing an internal duct plate made access for cleaning easier. Sorry, have no pictures of the internals, as my hands were as dirty as the internals of the valve.
Final clean was by steam cleaning using a pressure washer. Oiled the valve stem and assembled the EGR valve.
I checked out the electrics of the actuator and it tested OK.
Pin out for the Pierburg EGR valve fitted to the Smart for 2 Cdi is as follows:

Pin 1 Ground coil
Pin 2 Wiper signal pot meter
Pin 3 Ground pot meter
Pin 4 Volt supply pot meter (5 V)
Pin 5 Volt supply coil (Battery voltage)

Measurements:
Between pins 1 and 5: 8.2 Ohm
Between pins 3 and 4: 2.7 kOhm

Fitted the EGR valve in the Smart with a brand new blanking piece made out of stainless steel. The good old Cdi does not report any faults when the exhaust supply to the EGR valve is blanked off. Unsure about the new Cdi.

Here is a picture of the cleaned out EGR valve complete with blanking piece and seal:

The duct plate can be removed to get better access.

Why would you want to blank off your EGR valve?

EGR is the worst contraption conceived my man and added to a diesel engine. Good on paper, but in practice and especially in older engine it is a real pain. Soot from exhaust mixes with oil vapour from the breather pipes and forms a hard deposit inside the inlet manifold that only elbow grease can shift. If left unchecked it will strangle the engine. EGR increases fuel consumption and reduces power.

you do realise it doesnt matter what you do to try and increase the power that it will never match the remap ;-)

I don't believe in remaps and I don't need more power out of my Cdi. The existing power output is more than adequate for my needs. I want reliability and low fuel consumption. Remaps don't provide that.

remaps on diesels are different, you can get more power and better mpg.

Agreed, the CDI conrods are monstrous and the engines are bomb proof so I wouldn't be concerned at all about decreasing reliability. After having my petrol 450 remapped I was getting an extra 90 miles out of a tank of fuel.
A CDI can potentially get much more.

I am quite happy with my fuel consumption as I consistantly get between 65 and 85 MPG, all depending on my right foot and driving style. My MPG might now be slightly enhanced as a result of disconnecting the EGR - time will tell.

Correction.
Pin 1 is controlled ground coil.


Pin out for the Pierburg EGR valve fitted to the Smart for 2 Cdi is as follows:

Pin 1 Controlled ground coil
Pin 2 Wiper signal pot meter
Pin 3 Ground pot meter
Pin 4 Volt supply pot meter (5 V)
Pin 5 Volt supply coil (Battery voltage)

The "plate" on top left is a seal. "Plate" on top right is my DIY blanking plate. You can get seals for the dealer. Think you need to make your own blanking plate.

The purpose of the EGR blanking plate is to avoid the engine being strangled due to build up of soot in inlet manifold. There will also be less soot and acid forming in the engine oil so overall better lubrication.

Below photo shows where I fitted my blanking plate on turbo side of EGR feed pipe.

The photo shows my Smart 0.8 Cdi with turbo removed and relevant holes blanked (made me mobile whilst waiting on arrival of replacement turbo). EGR feed pipe is the stainless steel pipe in upper part of photo. Blanking plate is fitted between feed pipe flange and exhaust manifold/ turbine housing. This position results in less turbo lag, obviously provided a turbo is fitted.

Same engine with turbo fitted: