P0118

Engine Coolant Temperature (ECT) Sensor Circuit:

Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference and a ground to the ECT sensor. When the engine is cold, the sensor resistance will be high.
As the engine warms up, the ECT sensor resistance decreases and the voltage drops. At normal engine operating temperature, the voltage should be between 1.5 and 2.0 volts.
The engine coolant temperature sensor is one of the inputs used to control:
- The fuel delivery
- The Ignition Control
- The Evaporative Emission (EVAP) canister purge valve
- The Idle Air Control (IAC) valve

Conditions For Setting The DTC
- The engine run time is greater than 60 seconds.
- The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F).

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM 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.
- The PCM will default to 20°C for the first 60 seconds of engine run time for Engine Coolant Temperature (ECT). Then default to 92°C for engine coolant temperature. The scan tool will not 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.
- DTCs can be cleared by using a scan tool.

Diagnostic Aids
Normal operating temperature for the engine cooling system is between 90°C and 95°C.

DTC P0118 - Engine Coolant Temperature (ECT) Sensor Circuit High Voltage:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
11. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCM must be reprogrammed.