What Is This For

The EGR status is monitored by the ECM, that's why the following fault codes will be logged in case of the correspondent failure(extract from http://cdbl.free.fr/Nanocom/V1-V2/Manuels/Anglais/Nanocom%20user%20manual%20V1.2.pdf
APPENDIX TABLE 1: COMPLETE FAULTS CODE LIST , page 44-45):

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1-6 EGR inlet throttle short circuit (current)
1-7 EGR vacuum modulator short circuit (current)
7-6 EGR inlet throttle short circuit (logged)
7-7 EGR vacuum modulator short circuit (logged)
9-6 EGR inlett throttle open load (logged)
9-7 EGR vacuum modulator open load (logged)
20-4 EGR valve stuck open (logged)
20-5 EGR valve stuck closed (logged)
24-4 EGR valve stuck open (current)
24-5 EGR valve stuck closed (current)

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IMO the ECM will "know" about short or open circuits as for any other monitored circuit and throw the highlighted codes based on ECT, MAF and IAT readings which must be in conjunction with the EGR modulation percentual status.

on mine, with the original ECM(now i have a remapped one) when i first only unplugged and clogged the vacuum pipe on the EGR valve for test i've got the "EGR valve stuck closed" code without touching the modulator that's why i ended up at that conclusion

I have removed EGR plumbing but left modulator in place and connected. I occasionally get the stuck open and stuck closed faults. I assume the load sensed by the ECU is different without the vacuum supply available.

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Originally Posted by sierrafery

that's strange... and IMO not normal, is yours remapped?

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No remap AFAIK, but it was 9 years old when I got it. But if I had paid for a remap I'd be pretty disappointed with the end result.

I'd be surprised if the ECM bothered looking for any status of the EGR modulators.

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Originally Posted by kelvo

I'd be surprised if the ECM bothered looking for any status of the EGR modulators.

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I'd be surprised too, if Tombie says the ecu doesn't check for the absence of the unit.
Maybe if it's connected, the thing itself is able to detect egr stuck open/shut?
Try unplugging it and let us know what happens (no need to remove it permanently, if you are anxious).

I have my egr deleted and i always get the code that it is stuck open or closed. I clear it and then it comes back. It does no harm.