Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN4 from the PCB
Disconnect the connector from the low pressure sensor

Measurement:

Measure the resistance between the brown, blue and black wires of the low pressure sensor harness.
Expect continuity / zero resistance on each of the wires.
Also visually inspect the harness for good general condition.