The relay is driven by the DME control unit.
Function of main relay:
Voltage supply to all components in the engine electrical/electronic system
Perceivable effects: - Engine does not run
Fault codes can be entered in any combination in the fault code memory of the engine control unit if the system voltage was too low due to battery discharge or due to failure or contact fault of the DME main relay.
If fault code 27C4 main relay is stored in the DME, all fault code entries listed below that were stored at the same km reading (mileage) are to be ignored and deleted. The DME control unit should on no account be replaced.