P0684 Preheating control unit (feedback)

			Test results
1	COMPONENT CONCERNED	CONNECTIONS CHECK	OK (NO FAULTS DETECTED)	FAULT DETECTED	OPERATION
	Preheating control unit connections	Check that the connections are not faulty	Go to Step 2	Faulty connections	Restore the correct connections
2	COMPONENT CONCERNED	WIRING CHECK	OK (NO FAULTS DETECTED)	FAULT DETECTED	OPERATION
	Preheating control unit connections	Check the wiring continuity	Go to Step 3	Faults in the continuity of the wiring	Restore the correct continuity for the wiring
3	COMPONENT CONCERNED	WIRING CHECK	OK (NO FAULTS DETECTED)	FAULT DETECTED	OPERATION
	Preheating control unit connections	Check that the wiring is correctly insulated	Go to Step 4	Wiring insulation not correct	Restore the correct insulation for the wiring
4	COMPONENT CONCERNED	GLOW PLUG CONTROL UNIT OPERATION CHECK	OK (NO FAULTS DETECTED)	FAULT DETECTED	OPERATION
	Preheating control unit	Check that the preheating control unit is working properly	End of diagnosis	Preheating control unit not working correctly	Replace the preheating control unit Op. 5520C20