P0118

DTC P0118

Circuit Description

The engine coolant temperature (ECT) sensor is a variable resistor, 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 and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. 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. It the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets. The following table illustrates the difference between temperature, resistance, and voltage:






DTC Descriptors

This diagnostic procedure supports the following DTC. DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage


Conditions for Running the DTC

The engine is operating for more than 10 seconds.


Conditions for Setting the DTC

The ECT sensor temperature is less than -39°C (-38°F) for 45 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. 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 when the thermostat opens.

- Use the Temperature vs. Resistance Table to test the engine coolant temperature (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.

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

- If an intermittent condition is suspected, refer to Intermittent Conditions.Symptom Related Diagnostic Procedures


Test Description

DTC P0118 Steps 1-7:

DTC P0118 Steps 8-15:

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

5. This step isolates the condition. If the temperature changes, test for a condition in the low reference circuit. If the temperature remains the same test the signal circuit for a condition.

6. This step tests for the correct 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.