Engine - Coolant Temperature Sensor/Switch: Testing and Inspection

Fig. 3 Testing Thermo Switch:

1. Disconnect battery ground cable.
2. Drain cooling system.
3. Disconnect thermo switch connector from thermo switch.
4. Remove thermo switch from thermostat case.
5. Immerse switch in water up to level shown in Fig. 3, then connect suitable ohmmeter.
6. Heat water gradually, noting if there is no continuity (switch Off) when water temperature is under 190°F and continuity (switch On) when temperature is above 199°F.
7. If specifications are not as noted, replace switch.