HM95

Help please! I had a full service done 1 month ago and now this light has come up twice when driving on the motor way. It disappears straight away when turning the engine off and on. i've checked the oil and its totally fine so maybe the sensor? Garage cant do anything without the light being on and Honda dealer cant fit me in for over a month AND want the light on. The oil is fine, i've double checked it. Any ideas? thanks!