Main relay: Diagnostics

If there is an open circuit or short circuit to ground, diagnostic trouble code P1652 will be generated.
If there is a short circuit to B+, diagnostic trouble code P1653 will be generated.
If the current to control module pin 1 is missing, diagnostic trouble code P1640 will be generated, the throttle will close and the engine will stop.
NOTE: In Trionic T7, the main relay is always active when the ignition on. The current from the main relay can be read with the diagnostic tool.