This is an epsilonian device, although where the name comes from is still a mystery. It fakes the output of the MAF to make it look as though the EGR is still working. Sounds a little dodgy to me.
For $deities sake, people, it's a CEL, a Check Engine Light, not a cell which is part of the battery, or of the catalyst.
I have the <obscenity> EGR valve disabled by disconnecting the electrical connector to the N18 control valve. I don't get a CEL, but I expect there is a fault code stored in the ECU. I'll reconnect the N18 valve before it goes for service.
EGR is about reducing NOx emissions by keeping the combustion temperature down under part-load. The method used, rebreathing exhaust gas, is extremely unpleasent and contributes to major problems as the engine gets older, clogging the inlet manifold and the valve eventually sticks open to cause limp mode.
I'm not convinced by the arguments about NOx, as there is considerable research showing that reducing NOx while increasing CO and soot production (which is what the EGR does, as well as reducing efficiency) has an overall negative impact on the environment.