What is the "service vehicle soon"..? When I start my car it comes at the time.

Service engine soon is the equivalent of Check Engine or MIL light on other cars it's just bad terminology by Olds. A scan tool is needed to retrieve codes stored in the computer of your car indicating where the problem may be. When the Check Engine light comes on in some cars they are smart enough to put the car in limp mode , reduce power out put or disable air conditioning to lessen damage to the engine depending on how serious it things the problem may be. Get it checked out as it is a problem!