1.) Has the pressure sensor harness been disconnected at the pressure sensor or at the Main PCB. Also check for a loose connection.

2.) Unplug the unit. Take a resistance reading from the Main PCB. VIOLET to SKYBLUE should read 20 to 25 ohms. If the resistance is okay, proceed to the next step. If an open is read, disconnect the harness from the pressure sensor and check resistance again. if the resistance is okay, suspect a harness issue. If the resistance still reads open, replace the pressure sensor.

3.)  Plug in the unit and turn the unit on. With the pressure sensor connected, measure voltage from YELLOW to VIOLET and YELLOW to SKYBLUE. Both should read 2.5-3Vdc.

4.)  Inspect the pressure sensor hose for a blockage.