Powertrain Management (CNG)

DTC P0118

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. The ECT thermistor has high resistance when cold and low resistance when hot. The powertrain control module (PCM) supplies about 5 volts on the ECT signal circuit. The PCM also supplies a ground circuit to the ECT sensor. When the ECT resistance is high the ECT signal voltage remains near the supplied 5 volts. As the ECT sensor warms and resistance drops, more signal circuit voltage is pulled lower to the sensor ground. The PCM and the alternative fuels ECM monitor the ECT signal circuit voltage in order to determine the engines temperature.


This DTC sets when the ECT signal circuit voltage is above the normal operating range of the sensor.


Conditions for Running the DTC

* The engine is operating on alternative fuel.
* The engine has been operating for greater than 5 seconds when the intake air temperature (IAT) is greater than 0°C (32°F).
or
The engine has been operating for greater than 10 minutes when the IAT is less than 0°C (32°F).



Conditions for Setting the DTC

The Alternative Fuels ECM monitors an ECT sensor signal voltage of greater than 4.8 volts for at least 5 seconds continuously.


Action Taken When the DTC Sets




* A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
* The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
* The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.



Conditions for Clearing the MIL/DTC




* The Last Test Failed status will clear when the DTC runs and passes.
* The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
* The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
* All DTC Information can be cleared with a scan tool.



Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the condition is present.
3. This step determines if the condition affects the PCM.
4. This step determines if the ECT sensor is the open condition.
5. This step determines if the sensor ground circuit is the open condition.
6. This step determines if the ECT signal circuit wiring is the open condition.
9. If the connector terminals pass inspection test the sensor signal circuit for a short to a 5-volt reference circuit. Although an unlikely failure, this condition should be diagnosed before replacing the PCM.