Hi Steve
In my code breaker book it reads as below.
The voltage, frequency or value of control in the regulator circuit is incorrect (under fault ) Signal could be out of normal operating range, constant value, non-existent, corrupt, Possible fault regulator or wiring.
Eg regulator power supply short/open circuit, high circuit resistance or incorrect regulator resistance.
Note the control unit could be providing the correct signal but it is being affected by the circuit fault.
So pretty much what Brian as said already
