Circuit Description
The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.
The following table illustrates the difference between temperature, resistance, and voltage:
ECT | ECT Resistance | ECT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
DTC Descriptors
This diagnostic procedure supports the following DTC.
DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
Conditions for Running the DTC
The engine is operating for more than 10 seconds.
Conditions for Setting the DTC
The ECT sensor temperature is more than 139°C (282°F) for more than 45 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
| • | An overheating condition may cause this DTC to set. |
| • | After starting the engine, the ECT should rise steadily to about 90°C (194°F), then stabilize when the thermostat opens. |
| • | Use the Temperature vs Resistance Value Table in order to test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature Versus Resistance . |
| • | If the malfunction is not present at this time, refer to DTC P1114 . |
| • | If you suspect an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If you can only repeat DTC P0117 by duplicating the Failure Records, refer to Temperature vs Resistance. The table may be used in order to test the ECT sensor at various temperatures, in order to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the ECT sensor. If the ECT sensor appears OK, the malfunction is intermittent. Refer to Diagnostic Aids.
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When testing ECT signal circuit for a short to ground, you may need to inspect for continuity between all other PCM circuits.
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This vehicle is equipped with a PCM that utilizes an electrically erasable programmable read-only memory (EEPROM). When you replace the PCM, you must program the new PCM.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Is the temperature more than the specified value? | 138°C (280°F) | Go to Step 4 | Go to Step 3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Is the temperature less than the specified value? | -38°C (-36°F) | Go to Step 6 | Go to Step 5 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 | |
6 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | |
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 |
9 | Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? | -- | System OK | |
