P0118

DTC P0118 ECT Sensor Circuit High Voltage




Circuit Description
The Engine Coolant Temperature (ECT) sensor contains a device which changes its resistance based on temperature. This device is called a thermistor. The ECT sensor is mounted in an engine coolant passage. The ECT sensor has a signal circuit and a ground circuit. The VCM applies a voltage (approximately 5 volts) on the signal circuit to the sensor. The VCM monitors the changes in this voltage caused by changes in the resistance of the sensor. This allows the VCM to determine coolant temperature.

When the coolant is cold, the sensor resistance is high. The VCM will detect a high signal voltage due to this high resistance. This signal voltage is converted by the VCM into temperature. A high signal voltage will be seen on a scan tool as a low temperature.

When the coolant is warm, the sensor resistance is low. The VCM will sense a low signal voltage which is converted by the VCM into a higher temperature. At normal operating temperature, the VCM should measure about 1.5 - 2 volts on the ECT signal circuit.

This DTC is designed to detect an ECT sensor signal voltage higher than the possible range of a normally operating ECT sensor.

Conditions for Running the DTC
The engine has been running for more than 5 seconds.

Conditions for Setting the DTC
The ECT sensor voltage is greater than 4.9 volts for more than 20 seconds.

Action Taken When the DTC Sets
- The VCM illuminates the MIL (Malfunction Indicator Lamp) if a failure is detected during 2 consecutive key cycles.
- The VCM will set the DTC and records the operating conditions at the time the diagnostic fails. The VCM stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
- The VCM turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
- A history DTC will clear if no fault conditions have 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 is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.

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 Temperature vs Resistance.

An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.

Steps 1 - 3:

Steps 4 - 10:

Steps 11 - 14:

Steps 15 - 16:

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.