The check engine light, one of several warning lights that can illuminate on you cars dash board. This light is a warning that the engine is not operating at full capacity and the emissions system is not meeting Government requirements. In many cases the vehicle may run fine, yet the light is on. The light indicates that one of many systems is malfunctioning. On the other hand the engine may run rough when the light comes on and this indicates that the engine is misfiring. When this occurs the check engine light may flash on and off. This is a warning that the vehicle needs to be shut down or more severe damage to the emission system and engine will occur. Regardless, the vehicle needs to be repaired to proper working order. Letting it go and not repairing it will only compound the problem and lead to further damage to other systems. Think of it as if it were a football team, if one play is not up to par the whole team is affected.