Return water temperature sensor is shorted. '0' Ohm
1. Disconnect harness from Return Temperature Sensor. Measure resistance across sensor terminals. Is resistance less than 50 ohms?
Yes: Replace Return Water Sensor
No: -> 2
2. Disconnect harness from Control Module J5. Measure resistance between brown wires at terminals J5-4 and J5- 12. Is resistance less than 50 ohms?
Yes: Replace wires
No: Replace Control Module