Parking brake
Check the circuits for shorts and breaks. The signal on coordinator pin A13 (pin 77 on earlier models of coordinator) should be low and the signal on coordinator pin A23 (pin 20 on earlier models of coordinator) should be high only when the parking brake is applied. When the parking brake is released, the relation should be the opposite.
What you'll see
No driver-visible symptom recorded.
System reaction
No system-reaction text recorded.
Diagnostic depth
The parking brake circuit has one pressure monitor which monitors a high air pressure, and one which monitors a low air pressure. The pressure monitors communicate with the coordinator via signals, and in this case the signals have been implausible in relation to each other.
The pressure monitor for the higher air pressure has indicated that the parking brake is applied (active low), and the pressure monitor for the lower pressure has indicated that the parking brake is not applied (also active low).