P0118

CIRCUIT DESCRIPTION
The engine coolant temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

CONDITIONS FOR RUNNING THE DTC
The engine has been running for more than 60 seconds.

OR:

The engine run time is less than 60 seconds when the intake air temperature (IAT) is more than 0°C (32°F).

CONDITIONS FOR SETTING THE DTC
The ECT sensor temperature is less than -39°C (-38°F) for 20 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.
^ Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
^ If a short to a separate 5-volt source occurs, this DTC may set.
^ After starting the engine, the ECT should rise steadily, then stabilize when the thermostat opens.
^ Use the Temperature vs. Resistance Table in order to test the ECT sensor. A skewed sensor could result in poor driveability conditions. Refer to Temperature vs Resistance.
^ If a malfunction is not present at this time, refer to DTC P1115. P1115
^ If the condition is suspected of being intermittent, refer to Intermittent Conditions.

TEST DESCRIPTION

Steps 1-8:

Steps 9-14:

The numbers below refer to the step numbers on the diagnostic table.
3. The Temperature vs Resistance table may be used to test the ECT sensor at various temperatures to evaluate the possibility of a skewed sensor. If the ECT sensor appears to be OK, the malfunction may be intermittent. Refer to Diagnostic Aids.
4. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
10. The PCM in this vehicle use an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.