Cause of error code E52

Return Sens Open. 

Solution for error code E52

1. Is harness plugged into Return Temperature Sensor Is harness plugged into Control Module J5?
Yes: -> 2.
No: Insert Harness.

2. Check continuity of brown wires between Return Temperature Sensor and Control Module J5-4 and J5-12 Continuity?
Yes: -> 3.
No: Replace Wires

3. Measure Return Temperature Sensor resistance with digital meter. Estimate Sensor temperature. Do temperature and resistance fall within ranges? 
Yes: Replace Control Module.
No: Replace Return Temperature Sensor.