Engine light

Early last autumn, on one of our regular visit to check van in storage, on starting the engine we noticed the the little engine light came on, phoning the dealer/machanic he said to take it for a run as this sometimes happens with motorhomers when they have been standing, 

we done this but it didn't go out, so it was booked in for further investigation,  problem solved with new parties and repair, after a few mths it came on again so off on another short run and yes it went off( great) this week now !!!! yes you got it back on again, so on the phone this time explained everything, then we got asked have we disconnected the battery at all,? No o k he said has this sometimes happens when owners disconnect the battery for winter, it's booked in to be soughted but has any other motorhome owner experienced this ?