Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to the PCM. When the engine is cold, the sensor resistance is high, therefore the PCM will see a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. The voltage measured across the thermister is interpreted as a temperature.
Conditions for Running the DTC
The ignition switch in the on position.
Conditions for Setting the DTC
The engine coolant temperature is greater than or equal to 151°C (304°F) for 2 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip the diagnostic runs and fails. |
| • | A History DTC will clear after forty consecutive warm-up cycles, if this or any other emmision related diagnostic does not reort any failures. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after three consecutive trips without a fault condition. |
| • | A History DTC will clear after forty consecutive warm-up cycles during which the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from the start up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle). |
| • | Use of a Scan Tool will clear DTC codes. |
Diagnostic Aids
Check the harness routing for a potential short to ground. After the engine has started, the ECT temperature should rise steady to about 85°C (185°F). A mis-scaled sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the fault is still present, the engine coolant voltage will be greater than 151°C (303°F).
-
This test simulates a DTC P0117. If the PCM recognizes the high signal voltage (low temperature) the PCM and the wiring are okay.
-
This step will determine if the problem is a short to ground or a malfunctioning PCM.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing any DTCs, use the scan tool to save the Freeze Frame and the Failure Records for reference.The control module's data is deleted when the DTC Clear Information function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool display an ECT greater than or equal to the specified value? | 151°C (303°F) | |||
Does the scan tool display an ECT a temperature colder than or equal to the specified value? | -30°C (-22°F) | |||
Is the resistance at the specified value? | Infinite | |||
5 | The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If the additional DTCs are stored, refer to those tables first. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | Go to Diagnostic Aids |
6 | Repair the short to the ground in the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
7 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
8 |
Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Is the action complete? | -- | -- | |
9 |
Does the scan tool indicate this diagnostic Passed? | -- | ||
10 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to The Applicable DTC Table | System OK |
