P0117

DTC P0117 ECT Sensor Circuit Low Voltage






Circuit Description

The Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to the PCM. When the engine is cold, the sensor resistance is high, therefore the PCM will see a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. The voltage measured across the thermister is interpreted as a temperature.

Conditions for Running the DTC

The ignition switch in the on position.

Conditions for Setting the DTC

The engine coolant temperature is greater than or equal to 151°C (304°F) for 2 seconds.

Action Taken When the DTC Sets

^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic tails. The first time the diagnostic fails, the Failure Records store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL off after three consecutive trips without a fault condition.
^ Use of a scan tool will clear DTC codes.

Diagnostic Aids

Check the harness routing for a potential short to ground. After the engine has started, the ECT temperature should rise steady to about 85°C (185°F). A mis-scaled sensor could result in poor driveability complaints. Refer to Temperature vs Resistance.

Test Description

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

2. It the fault is still present, the engine coolant voltage will be greater than 151°C (303°F).
3. This test simulates a DTC P0117. If the PCM recognizes the high signal voltage (low temperature) the PCM and the wiring are okay.
4. This step will determine if the problem is a short to ground or a malfunctioning PCM.