The computer in your Volvo controls many critical vehicle system functions like air-to-fuel mixture and generating and storing error codes. When there is regular maintenance that needs to be done or when something malfunctions or needs to be fixed on your Volvo, the computer sends a signal to the "check engine" light. When you fix the vehicle or complete the regular maintenance, the code is still stored on the computer and the engine light will stay lit until the codes are cleared and the computer is reset.
Open the bonnet of your Volvo and loosen the retaining nut on the cable clamp running to the negative battery terminal using a socket wrench.
Slide the cable clamp off the negative battery terminal.
Wait five seconds and reconnect the cable clamp.
Tighten the retaining nut on the clamp using a socket wrench.
For specific information about your Volvo's computer, consult the particular vehicle's manual (see Resources).