Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference and a ground to the ECT sensor. Whenever the engine is cold, the ECT sensor resistance will be high.
As the engine warms up, the ECT sensor resistance decreases and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts.
The engine coolant temperature sensor is one of the inputs used to control the following items:
| • | The fuel delivery |
| • | The Torque Converter Clutch (TCC) |
| • | The Ignition Control (IC) |
| • | The Evaporative Emission (EVAP) canister purge valve |
| • | The Idle Air Control (IAC) valve |
Conditions For Setting The DTC
| • | The engine run time is greater than 128 seconds. |
| • | The ECT sensor indicates that the engine coolant temperature is greater than 138°C (280°F). |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) illuminates. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information. |
| • | A history DTC is stored. |
| • | The PCM defaults to 20°C for the first 60 seconds of engine run time. After 60 seconds the ECT will default to 92°C for engine coolant temperature. The scan tool will not show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
After the engine has started, the ECT should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
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This step simulates a DTC P0118. If the PCM senses the change, then the PCM and the ECT wiring are OK.
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The replacement PCM must be programmed and the crankshaft position variation procedure must be performed. Refer to the latest Techline procedure for PCM reprogramming and also refer to Powertrain Control Module (PCM) for the Crankshaft Position Variation Procedure.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
2 |
Is the ECT sensor value greater than the specified value? | 130°C (266°F) | ||
3 |
Is the ECT sensor value greater than the specified value? | 130°C (266°F) | Go to Diagnostic Aids | |
Disconnect the ECT sensor electrical connector. Is the ECT sensor value less than the specified value? | -30°C (-22°F) | |||
5 | Check the ECT sensor signal circuit for a short to ground and repair as necessary. Was a repair necessary? | -- | ||
6 | Replace the ECT sensor. Is the action complete? | -- | -- | |
Replace the PCM. Is the action complete? | -- | -- | ||
8 |
Does the scan tool indicate that the diagnostic ran and passed? | -- | ||
9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
