Volvo: Oil leak?, blown head gasket, power management system

Question
I have a 2000 s70 volvo. I keep losing oil but have no visible oil leak. I put oil in and tried to shut off check engine light, but it won't go off. It has 105,000 miles. Can it be something to do with pistons or something more serious.

Answer
Albert,
Since there is no sign of an oil leak you maybe "using" oil! That could mean bad valve guides, or seals, turbo(if equipped), blown head gasket and oil is leaking into the cooling system, even worn piston rings. That will take some inspection time. Get the car to a Volvo shop and see what they find. If the check engine light is on, that means there is a fault code stored in the power management system and that needs to be read and repaired. That however will not have any effect on the oil lose.