Wrench/service light comes on when accelerating uphill on highway?

When I accelerate to overtake on the highway uphill the wrench icon / service light lights up for a few seconds then goes away, I can't say the car feels any different when it happens, it has sometimes happened going on a flat road and also happens if I use cruise control to accelerate fast uphill, it has only happened in 4th-6th gear when going around 80 km/h - 50mph and above, the car has had service between the time I first noticed it and now. If I slowly accelerate it doesn't happen, though it has happened one time before that it lit up when I was in cruise control. It's a diesel engine.