A bit of an essay below but what else do you want to read first thing on a Monday morning.
I have been thinking if there is a more elegant way to keep the EGR valve shut other that
going to the trouble of puting in the blanking plate, then having to remove it every time for a service.BTW, we are talking about the 2010 MN 2.5 turbo here.
So I had a look at one of the older workshop manuals  available on the internet showing the electrical connections to the EGR valve. Unfortunatelly either the connection diagram to test it or the test procedure itself is incorrect, and to make things worse the English is rather jiberish to say the least.
So being the world best electrical engineer [well in my mind anyway!] I proceeded to disconnect the plug to the EGR and conect a 5V power supply between pins 4 & 6 on the EGR connector [+ on pin 6 and - on pin 4]. Every time I applied the voltage I could hear the EGR valve/motor open and stay open as long as the + 5V remained. When the supply voltage was removed it appeared that the EGR closed again. Hm....................
OK then so I proceded to investigate what signal is sent back to the ECU to tell it the EGR has opened. This is where the workshop manual is confusing, but eventually worked out that a +5v signal appears on pin 1 when the EGR opens.
Great, all looking cool now, I am so good and know what to do
Made up a simple circuit using a 12V relay and connected it onto the EGR plug going back to the ECU.
Basically the relay coil was connected between pins 4 & 6 on the plug, the reasoning being this is that when the EGR is commanded to open, the 12V relay will activate right?
Then connected the N/O relay pins between 1 & 3. Pin 3 on the plug has a constant +5V so when the relay activates
it simply send the +5V to pin 1 and back to the ECU to tell its open. Basically 4 wires going back into the EGR plug.
Having done this, I took the car out for a drive untill it reached operating temp, gave it a few bootfulls etc. All was good
no engine error codes showing with improved throttle response etc as already correctly pointed out by other members.
The one thing I did notice was when I turned the vehicle off, the engine no longer shut down smoothly but with sudden vengeance but anyway I thought who cares. Drove it again later on last night and it was fine.
So I thought all is good until this morning when I started the car and the engine light remain on
Drove to work fine, lots of power etc with the engine light on. Wonder why this morning and not last night
What can I deduce from all of this, given that I have little or no technical information on the MN as to exactly how the EGR is commanded to open, I need to know the exact voltage sent by the ECU to the EGR motor/valve and furthermore what feedback is expected to be seen be the ECU, but I can only conclude the following:
My assumption is incorrect and the ECU drive voltage to the EGR is much less than 12V therefore not activating my 12V relay relay, and in turn the ECU not being sent back a +5V signal.....................???? which is the reason behind the engine check light error. I hope its that simple.
Does anyone out there have detailed information on EGR operation, someone with Mitsubishi workshop manual knowledge!
If I could get this information, I can then design a proper circuit to attach to the EGR plug, eliminating the need for the blanking plate and making the process of removing the realy before a service a 5 second job