P0118

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the VCM. The VCM applies a voltage on a 5 volt reference circuit to the sensor. When the engine coolant is cold, the sensor's internal resistance is high resulting in a high voltage ECT Sensor Signal. As the engine coolant temperature increases, the sensor's internal resistance and ECT Sensor Signal decrease.

CONDITIONS FOR SETTING THE DTC

^ The engine run time is greater than 5 seconds

^ The ECT signal voltage is greater than 4.90 volts

ACTION TAKEN WHEN THE DTC SETS

The VCM turns ON the MIL when this DTC is reported and 1 failure has occurred.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trip5 when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions t0ave been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

DIAGNOSTIC AIDS

Check the harness routing for a potential short to ground in the 5 volt reference circuit. After starting the engine, the temperature should rise steadily to about 90°C (194°F), then stabilize when the thermostat opens.

Use the Temperature vs Resistance Value table in order to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could result in poor driveability complaints. Refer to Specifications / Electrical / Temperature vs Resistance.

TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table.

2. If the fault is present, the engine coolant temperature voltage measures greater than 4.90 volts.

3. This test simulates the conditions for a DTC P0117. If the VCM recognizes the grounded circuit (low voltage) and displays a low voltage message, the VCM and the wiring are okay.

4. This test checks for an open or grounded signal sensor circuit. Also being checked are the ECT sensor ground circuit and the VCM.

5. This test checks for a short to voltage on the ECT signal circuit.

12. After repairing a short to voltage, it is necessary to recheck the operation of the ECT sensor.