D4: Check Harness GND Continuity

Measure the resistance between EM013/027 & PI026/002; Repeat for EM013/027 & PI027/002

Is the resistance < 0.5 ohms?

Yes
Go to D5

No
Inspect connectors EM013 & PI026 for corrosion, damaged or pushed back pins or repair the harness/connector PI001/018; test the system for normal operation.