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 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, this Diagnostic Trouble Code (DTC) will set.

CONDITIONS FOR RUNNING THE DTC
The engine is running for more than 15 seconds.

CONDITIONS FOR SETTING THE DTC
The ECT sensor temperature is less than -38°C (-36°F) for more than 24 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ First failure:
- The MIL is not turned ON.
- A DTC is stored in memory under Failed Last Test.
- The Failure Records are stored.
^ Second consecutive drive cycle with a failure:
- The MIL is turned ON.
- A DTC is stored in memory under history.
- The Freeze Frame data is stored.
- The Failure Records are stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
^ The history DTC will clear if the fault conditions have not been detected for 40 warm-up cycles.
^ A scan tool can be used to clear DTC information.

DIAGNOSTIC AIDS
If a short to a separate 5-volt source occurs this DTC may set, if this is found to be the problem a continuity test to all other PCM circuits will be necessary to diagnose the specific circuit.

After starting the engine, the ECT should rise steadily to about 90°C (194°F) then stabilize after the thermostat opens.

Use the Temperature vs Resistance Table in order to test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature vs Resistance.

If a malfunction is not present at this time refer to DTC P1115. P1115

If an intermittent condition is suspected refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-7:

Steps 8-13:

The numbers below refer to the step numbers on the diagnostic table.
4. This step 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.