P0118

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls the signal voltage to the Powertrain Control Module (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 thermistor is interpreted as a temperature.

CONDITIONS FOR RUNNING THE DTC
The engine has been operating for at least 8 minutes.

CONDITIONS FOR SETTING THE DTC
^ The ECT is less than 30°C (-22°F).
^ The conditions were met for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
Check the harness routing for a potential short to voltage. After the engine is started, the ECT temperature should steadily increase to approximately 85°C (185°F). A mis-scaled sensor could result in poor driveability complaints.

TEST DESCRIPTION

Steps 1-4:

Steps 5-15:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if DTC P0118 is a hard failure or an intermittent condition.
3. This step will determine if there is a wiring condition or a malfunctioning PCM.
9. This step determines if there is a short to voltage on the signal circuit. A short to voltage increases the current flow through the sensor, which overwhelms the sensor. This does not allow the sensor to pull down the circuit to the correct voltage and thus display the correct temperature.
10. After repairing the short to voltage, check the sensor for proper operation.