Donny Q, I too have a '99 Discovery, what I would do, is pull the cables off of the engine batteries, over night. I had a problem with check engine light on my Jeep, GC, and that's what I did, it reset the ECM. I don't know for sure if the Cummins, will reset the ECM, but maybe worth a try?
'05 Monaco Beaver 400 Quad SLD 400hp C-9 Caterpillar
2014 Grand Cherokee, Limited, diesel
Katie-Doberman Pinscher, Tigger, yellow Tabbycat.