The ECM provides ground to one side of the coil of the main relay and the other side is connected to the battery. The ECM monitors battery voltage and the voltage after the main relay.
During engine running, if system voltage is above 17V, ECM sets P0563.
Item
Detecting Condition
Possible cause
DTC Strategy
Signal check, high
Poor connection
Short in circuit
Faulty charging system
Faulty main relay
Faulty ECM
Enable Conditions
After Start > 120 sec
Vehicle speed > 16 kph
Threshold value
System voltage > 17V
Diagnosis Time
Continuous
MIL On Condition
No MIL