P0117

P0117 Engine Coolant Temperature Low Voltage




Circuit Description
The Engine Coolant Temperature (ECT) Sensor uses a thermistor to control the signal voltage to the powertrain control module (PCM)/engine control module (ECM). The PCM/ECM supplies a voltage on the signal circuit to the sensor. When the air is cold, the resistance is high; therefore the ECT signal voltage will be high.

As the engine warms, the sensor resistance becomes less and the voltage drops. At normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.

The ECT sensor is used to control the following items:
- Fuel delivery.
- Ignition.
- Evaporative (EVAP) Emission canister purge valve.
- Idle Air Control (IAC) valve.
- Electric cooling fan.

Conditions for Setting the DTC
- Engine run time is greater than 120 seconds
- ECT is greater than 135 °C (275 °F)

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history Diagnostic Trouble Code (DTC) is stored.
- Both Cooling fan turns on.
- The PCM/ECM will default to 68 °F (20 °C) for the first 60 seconds of engine run time and then to 198 °F (92 °C). The scan tool may show the defaulted value.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
After the engine has started, the ECT should rise steadily to about 194 °F (90 °C) then stabilize when the thermostat opens.

Use the Temperature vs. Resistance Values table to evaluate the possibility of a skewed sensor. Refer to "Temperature vs. Resistance".

Step 1 - 9:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
4. This step simulates a DTC P0118 condition. If the PCM/ECM senses the change, then the PCM/ECM and the ECT wiring are OK.
7. The replacement PCM/ECM must be reprogrammed. Refer to the latest Techline procedure for PCM/ECM reprogramming.