Coolant Temperature Sensor Test

Fig. 51 Coolant Temp. Sensor Resistance Values:

1. Run engine at idle speed and disconnect plug from coolant temperature sensor. Simulate a coolant temperature of 20°C by connecting a resistance substitution unit set to 2.5 kOhm to coolant temperature sensor plug and ground. If idle speed increases, proceed to step 2. If idle speed does not increase, repair open circuit.
2. Sut off engine. Check resistance of coolant temperature sensor between sensor terminal and ground at two temperatures. See Fig. 51 for a resistance vs. temperature graph. If sensor tests ok, proceed with step 3. If sensor tests bad, replace it.
3. Turn ignition on and check voltage between temperature sensor plug and ground. If voltage reading is approximately 5 volts, the system tests good and the test is completed. If voltage reading is not approximately 5 volts, check for and repair open circuit as needed. If wiring is good, replace idle speed control unit.