P0117

DTC P0117 Engine Coolant Temperature Low Voltage

Circuit Diagram:

Circuit Description
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM supplies a 5 volt reference and a ground to the sensor. When the engine coolant is cold, the resistance is high; therefore the ECT signal voltage will be high. If the engine coolant is warm, sensor resistance becomes less; therefore the IAT signal voltage drops. At normal engine operating temperature, the voltage will be between 1.5 to 2.0 volts at the ECT signal terminal. The ECT sensor is used to control following items:
- Fuel delivery.
- Ignition.
- Evaporative (EVAP) Emission canister purge valve.
- Idle Air Control (IAC) valve.
- Electric cooling fan.

Conditions for Setting the DTC
- ECT is greater than 149 °C (300 °F)
- Engine run time is greater than 120 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The 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 DTC is stored.
- Both cooling fans turns on.
- The ECM will default to 20 °C (68 °F) for engine coolant temperature for the first 60 seconds of engine run time and then 92 °C (198 °F). The scan tool will not show the defaulted value.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after four 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.
- Disconnecting the ECM battery feed for more than 10 seconds.

Diagnostic Aids
After engine start the ECT should rise steadily to 90 °C (194 °F) 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. [1][2]Computers and Control Systems

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 ECM senses the change, then the ECM and the ECT wiring are OK.
7. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.

Step 1 - 5:

Step 6 - 9: