LR3 check engine light

[Disco96JSWB]

Started LR3, waiting for son to come out of house, opened hood since it had been a few months since I last saw so much plastic, closed it, got back in car and check engine light was on.
Drove around for a couple of days, played with fuel cap, light was still on.
Opened hood (all right, bonnet), slammed it, no light.

[rvrsrvc]

Not sure what the issue is here: you "checked the engine"......