Engine Coolant Temperature Sensor High Voltage

Diagnostic Trouble Code (DTC) P0118

Engine Coolant Temperature Sensor High Voltage



                                                                                              Circuit Knowhow


  • A thermistor is made use of by the Engine Coolant Temperature sensor (ECT for regulating the signal voltage going to the engine control module (ECM.
  • A reference voltage on the signal circuit to the sensor is supplied by the ECM.
  • The ECT signal voltage will be high when the engine coolant is cold and the resistance is high.
  • The ECT signal voltage will fall when the engine is warm and the resistance will be low.
  • The voltage will dwell round 1.5 and 2.0 volts if measured at the ECT signal terminal at normal engine operating temperature.



The ECT sensor is used in the following:

  1. Fuel delivery.
  2. Lock Up Clutch (LUC).
  3. Ignition.
  4. Evaporative Emission (EVAP) Canister Purge Valve.
  5. Electric cooling fan.



Time when DTC sets

Task Boosted when DTC sets

What clears DTC

1) When ECT voltage is > 4.98V.

1) The Malfunction Indicator Lamp (MIL) will be seen glowing.

1) The MIL will turn off after four repeated ignition cycles in which the diagnostic runs perfectly.



2) The ECM will start noting operating conditions since when the diagnostic fails which will be stored in the Freeze Frame and Failure Records will be sparked.


2) A history DTC will vanish after 40 consecutive warm-up cycles.



3) A history DTC will be recorded

3) DTC(s) can be cleared by using the scan tool.



4) The ECM will replace a fixed MAP value and use TP to control the fuel delivery.

 Note: The scan tool will not highlight this defaulted value.


4) Disconnecting the ECM battery feed for a time beyond 10 seconds will clear the DTC.


5) The coolant fan will turn     ON.





                                                    Diagnostic Aids


  1. Once the engine has been made to start, the ECT is expected to rise steadily till it reaches about 90°C (194°F) before stabilizing when the thermostat opens.
  2. Consult the temperature vs. Resistance values table to gauge and assess the likelihood of a skewed sensor.
  3. Refer to "Temperature vs. Resistance" in this section.