P0118

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Engine Coolant Temperature (ECT) sensor contains a semiconductor device which changes resistance based on temperature (a thermistor). The ECT sensor is mounted in the engine coolant pump housing. 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 changes in this voltage caused by changes in the resistance of the sensor to determine coolant temperature.

When the coolant is cold, the sensor (thermistor) resistance is high, and the PCMs signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM will sense a high signal voltage (low temperature). When the coolant is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense 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 20 seconds.

^ The PCM indicates Engine Coolant Temperature less than -40°C (-40°F).

^ All conditions met for 4.5 seconds.

ACTION TAKEN WHEN THE DTC SETS

^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

^ The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated.

^ The PCM will use a default engine coolant temperature.

^ Transmission torque converter clutch (TCC) will apply early.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

^ A last test jailed (Current DTC) will clear when the diagnostic runs and does not fail.

^ PCM battery voltage is interrupted.

^ Using a Scan tool.

DIAGNOSTIC AIDS

^ An intermittent may be caused by the following:

- Poor Connections.

- Mis-routed harness.

- Rubbed through wire insulation.

- Broken wire inside the insulation.

^ If other DTCs are set that share the same ground and/or 5.0 volt reference circuit, check for faulty connections and for faulty wiring.

^ If the engine has been allowed to sit 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 Table.

^ If it is determined that the DTC occurs intermittently, performing the P1107 diagnostic table may isolate the cause of the fault.

For intermittents, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to step numbers on the diagnostic table.

2. Determines if the malfunction is present. For any test that requires probing the PCM or a component harness connector, must use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent damage to the harness connector terminals.

3. Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed. refer to Symptoms. Testing and Inspection

4. If the engine coolant temperature goes above 150°C (302°F), indicates the PCM and ECT wiring is OK.

5. If the engine coolant temperature goes above 150°C (302°F), indicates the PCM and ECT signal circuit is OK.

6. Disconnecting the PCM will allow using the DVM (J 39200) to check continuity of the circuits. This will aid in locating an open or shorted circuit.

8. Disconnecting the PCM will allow using the DVM (J 39200) to check continuity of the circuits. This will aid in locating an open or shorted circuit.