P0118

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor 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.

^ Torque Converter Clutch (TCC).

^ Ignition Control (IC).

^ Evaporative Emission (EVAP) canister purge valve.

^ Idle Air Control (IAC) valve.

^ Electric cooling fan.

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 tails. This information will be stored in the Freeze Frame and Failure Records buffers.

^ A history DTC is stored.

^ Coolant tan turns ON.

^ The PCM will default to 20°C (68°F) for the first 60 seconds of engine run time and then to 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 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

^ Normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F).

Use the Temperature vs. Resistance table in Specifications to evaluate the possibility of a skewed sensor.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD 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 fault occurred. The information is then stored in the scan tool for later reference.

4. This step simulates a DTC P0117. It the PCM senses the change, then the PCM and the ECT wiring are OK.

11. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.