Circuit Description
The engine coolant temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high, therefore, the ECT signal voltage will be high.
As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.
The ECT sensor controls 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 |
| • | The electric cooling fan |
Conditions for Setting the DTC
| • | The engine run time is greater than 128 seconds. |
| • | The ECT is greater than 142°C (289°F). |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
| • | The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F). The scan tool may show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three 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. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
| • | After the engine has started, the ECT should rise steadily to about 90°C (194°F).Then, the ECT should stabilize when the thermostat opens. |
| • | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature vs Resistance . |
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 fault 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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Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
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 |
