Check the electrical connections if the coolant heater fails to heat the coolant. Check the following if the coolant heater fails to heat the coolant:

1. Check for 110 volt AC external power source.
2. Check for continuity to ground of heater cord.
3. Check for shorts to ground of heater cord.
4. Replace cord as required.
5. Check heater if the external power source and the cord are OK.
6. The heater should show continuity.
7. Replace as required.