P0118

Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor contains a semiconductor device which changes the resistance based on the temperature (a thermistor). The ECT sensor is mounted in the left bank cylinder head near the front of the engine. The ECT sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine the coolant temperature.

When the coolant is cold, the sensor (thermistor) resistance is high. The PCMs signal voltage is only pulled down a small amount through the sensor to a ground; therefore, the PCM senses a high signal voltage (low temperature). When the coolant is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount; therefore, the PCM senses a low signal voltage (high temperature). At normal operating temperature, the scan tool should display an ECT value of 1.5-2.0 volts.

When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC sets.

The engine coolant temperature information is sent to the instrument panel cluster via the class 2 circuit.

CONDITIONS FOR RUNNING THE DTC
The engine run time is more than 60 seconds.
OR
The engine run time is less than 60 seconds when the IAT is more than 0°C (32°F).

CONDITIONS FOR SETTING THE DTC
^ The engine coolant temperature is less than -39°C (-38°F).
^ All conditions met for 20 seconds.

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

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns the Malfunction Indicator Lamp (MIL) OFF after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.
^ For any test that requires probing the PCM or component harness connectors, use the J 35616-A connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

If the engine has sat overnight, the engine coolant temperature and intake air temperature values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature vs Resistance.

If you determine that the DTC occurs intermittently, performing the P1115 diagnostic table may isolate the cause of the fault.

For an intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures

TEST DESCRIPTION

Steps 1 - 8:

Steps 9 - 19:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the malfunction is present.
3. If DTC P1635 and P1639 set at the same time, this indicates that the signal circuit is shorted to a voltage.
4. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.
5. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor wiring is OK.
6. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor signal circuit is OK.
7. Disconnecting the PCM allows using the DMM in order to test continuity of the circuits. This aids in locating an open or a shorted circuit.
8. Disconnecting the PCM allows using the DMM in order to test for a short to voltage.