P0117

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 lower 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 less than 0.25 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 temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

Check for an intermittent short to ground in the ECT sensor signal circuit by moving the VCM harness at various locations and monitoring the ECT voltage on the scan tool. If the voltage varies, look for a short to ground in the area of the harness that caused the variance.

Use the Temperature vs. Resistance Value table 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 concerns. 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 still present, the ECT sensor voltage will measure less than 0.25 volts.
3. This test simulates a high signal voltage condition. If the VCM recognizes the high signal voltage and the scan tool display reads 4 volts or more, the VCM and the wiring are okay. While doing this test additional ECT related DTCs could set.
4. This test determines if the ECT sensor signal circuit is shorted to ground.