Cause of error code E40

Return water temperature sensor sees temperature higher than 200°F.

Solution for error code E40

1. Is correct harness connected to return sensor (2 Brown Wires)?
Yes: -> 2
No: Correct wiring

2. Unplug molex connector on return sensor. Is there moisture or liquid on metal pins? Liquid might be water or antifreeze solution. 
Yes: Remove all liquid from connector. Check for leaks. Repair all leaks. 
No: -> 3

3. Is Primary Pump properly oriented? 
Yes: -> 4
No: Install Primary Pump in proper orientation.

4. Disconnect harness from Return Water Sensor. Measure resistance using digital ohm meter. Is resistance between 950 to 33,000 ohms?
Yes: Replace Control Module
No: Replace Return Water Sensor