not relevant. the computer may have thought you had 80km lefy when you started, but when you are using gas idling, it sensing it isnt going anywhere, therefore you are getting 0km per gallon. the computer will than calulate you can go 0km on the remaining gas considering you have gone 0km in the last 30 minutes. it using past consumption to calcualte future consumption and since you were consuming without moving, it figured you would stay that way

as for having a bad cat, its very possible, but turbos will glow red when pushed. egt's can get hot enough to make iron glow. theres nothing wrong with it. now if the cat itself was glowing, id be a bit more concerned

 

The car is on the reserve tank and still showing 0, I have driven the car for 10km and nothing has changed, still showing as 0

 

Personally I wouldn't trust that mileage thingy as far as I can throw it. Mine has gone UP while driving to and from work before. I never understood why people insist on seeing how close they can come to running out of gas. I never let my tank get below 1/2 unless I'm adding something to the gas like Stabil or seafoam.

 

No doubt I don't trust the mileage thingy, I don't let the tank drain ever, I'm only doing it now so I can confirm the car is either drinking more fuel or possibly the sensor in the tank is gone