Control Module Power Supply: Diagnosis

If no current from either the +30 or +15 circuits is present, the engine will not start and the system cannot be contacted with the diagnostic tool.

Fig 1: Control Module Power Supply - Circuit Diagram
Courtesy of SAAB-SCANIA OF AMERICA, INC.

If no current is supplied to the control module from the main relay, diagnostic trouble code P1640 will be generated, the throttle will close and the engine will stop.