Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor that controls signal voltage to the powertrain control module (PCM). When the engine is cold, the sensor resistance is high, therefore the PCM will see high signal voltage. As the engine warms, sensor resistance becomes less and voltage drops. The voltage measured across the thermistor is interpreted as a temperature.
Conditions for Running the DTC
| • | The PCM performs this diagnostic trouble code (DTC) diagnostic continuously. |
| • | The ignition in the ON position. |
Conditions for Setting the DTC
| • | The engine coolant temperature is more than or equal to 151°C (303°F). |
| • | All of the diagnostic set conditions are met for 2 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Check the harness routing for a potential short to ground. After the engine is started, the ECT temperature should rise steadily to about 85°C (185°F). Refer to Symptoms - Engine Controls . A skewed sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance .
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 Testing for Electrical Intermittents in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the fault is still present, the engine coolant voltage will be greater than 151°C (303°F).
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This test simulates a DTC P0117. If the PCM recognizes the high signal voltage (low temperature), the PCM and the wiring are okay.
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This step will determine if the problem is a short to ground or a malfunctioning PCM.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the scan tool display an ECT greater than or equal to the specified value? | 151°C (303°F) | Go to Step 3 | Go to Step 5 | |
Does the scan tool display an ECT a temperature colder than the specified value? | -30 °C (-22 °F) | Go to Step 7 | Go to Step 4 | |
Does the resistance measure at the specified value? | ∞ | Go to Step 8 | Go to Step 6 | |
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 Diagnostic Aids | |
6 | Repair the short to the ground in the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 9 | -- |
7 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete replacement? | -- | Go to Step 9 | -- |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 |
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
