Circuit Description
The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. 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 high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.
Conditions for Running the DTC
The engine has been running for more than 60 seconds.
The engine run time is less than 60 seconds when the intake air temperature (IAT) is more than 0°C (32°F).
Conditions for Setting the DTC
The ECT sensor temperature is less than -39°C (-38°F) for 20 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
| • | If a short to a separate 5-volt source occurs, this DTC may set. If this is the problem, a continuity test to all other PCM circuits will be necessary in order to diagnose the specific circuit. |
| • | 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 Table in order to test the ECT sensor at various temperature levels and in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability conditions. Refer to Temperature Versus Resistance . |
| • | If a malfunction is not present at this time, refer to DTC P1115 . |
| • | If the condition is suspected of being intermittent, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If DTC P0118 can only be repeated by duplicating the Failure Records, refer to the Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures 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 to be OK, the malfunction is intermittent.
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Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
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The PCM in this vehicle use an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Is the ECT sensor temperature less than the specified value? | -38°C (-36°F) | Go to Step 4 | Go to Step 3 | ||||||
Does the DTC reset? | -- | Go to Step 4 | Go to Diagnostic Aids | |||||||
Is the ECT sensor temperature more than the specified value? | 138°C (280°F) | Go to Step 7 | Go to Step 5 | |||||||
5 |
Is the ECT sensor temperature more than the specified value? | 138°C (280°F) | Go to Step 7 | Go to Step 6 | ||||||
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 | ||||||
7 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||
8 |
Important: A sensor signal circuit shorted to a separate 5 V source will test the same as a bad ECT sensor and cause this DTC to set.
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||
9 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||
Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | |||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||
13 | With the scan tool, observe the stored Information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
