Volvo Self-Diagnostic System

System is capable of self-diagnostic functions through the use of Volvo diagnostic unit in engine compartment. System has 3 test modes. Test mode No. 1 is used to display and erase codes. Test mode No. 2 is used to verify operation of system components. Test mode No. 3 operates components in a certain order. Access to diagnostic system is provided by socket No. 2 on diagnostic unit with ignition on.