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 Running The DTC
The engine run time is more than 128 seconds.
Conditions for Setting the DTC
The ECT sensor indicates that the engine coolant temperature is more than 138°C (280°F) for 6.25 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order 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.
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when this DTC set. The scan tool stores this data for later reference.
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This step simulates a DTC P0118. The PCM and the ECT wiring are OK if the PCM senses the change in the ECT sensor signal.
-
Program the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Is the ECT sensor value more than the specified value? | 130°C (266°F) | ||
3 |
Is the ECT sensor value more than the specified value? | 130°C (266°F) | Go to Diagnostic Aids | |
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | |||
5 |
Was a repair necessary? | -- | ||
6 |
Was a repair necessary? | -- | ||
7 | Replace the ECT sensor. Refer to the Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
8 |
Was a repair necessary? | -- | ||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | ||
10 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
11 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
