P0118
Electrical Diagram:
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 voltage should measure about 1.5-2.0 volts at the PCM.
When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC will set.
CONDITIONS FOR SETTING THE DTC
^ Engine operating longer than 60 seconds
^ The PCM indicates Engine Coolant Temperature 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) when the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns the MIL OFF after three consecutive drive trips 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 forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ The PCM battery voltage is interrupted.
^ Use a scan tool in order to clear the MIL/DTC.
DIAGNOSTIC AIDS
^ The following may cause an intermittent:
- Poor Connections
- Mis-routed harness
- Rubbed through wire insulation
- Broken wire inside the insulation
^ 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. Specifications
^ If you determine that the DTC occurs intermittently, performing the P1115 diagnostic table may isolate the cause of the fault. P1115
For an intermittent, refer to Symptoms. Testing and Inspection
TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the malfunction is present. For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent damage to the harness connector terminals.
3. 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 will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616-A. Using this kit prevents any damage to the harness connector terminals.
4. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor wiring is OK.
5. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor signal circuit is OK.
6. Disconnecting the PCM allows using the DMM J 39200 in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.
8. Disconnecting the PCM allows using the DMM J 39200 in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.
11. Inspect for proper terminal tension/connections at the PCM harness before replacing the PCM.