P0118

Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor. The Control Module (PCM/VCM) supplies the ECT sensor with a reference voltage on the ECT signal circuit and a ground circuit. When the ECT sensor resistance is high (cold sensor) the ECT sensor signal voltage remains near the supplied voltage, and decreases the signal voltage as the ECT sensor resistance is low (warm sensor). The Control Module monitors the ECT sensor signal circuit voltage in order to calculate engine temperature.

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 more than 4.9 volts for more than 20 seconds

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

Conditions for Clearing the MIL/DTC
^ The Control Module 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 start-up 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
After starting the engine, the ECT sensor temperature should rise steadily to about 90°C (194°F), then stabilize when the thermostat opens. Check for an intermittent open or short to battery voltage in the ECT sensor signal circuit. This may be accomplished by moving the VCM harness at various locations while monitoring the ECT temperature and voltage on the scan tool. If the voltage varies, look for an open or short to voltage in the area of the harness that caused the variance.

Use the Temperature vs Resistance Value table in order to test the ECT 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. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. If the condition is present, the ECT sensor voltage measures more than 4.9 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 ECT sensor signal 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 sensor signal circuit.
12. After repairing a short to voltage, it is necessary to recheck the operation of the ECT sensor.