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 run time is more than 3 seconds.
Conditions for Setting the DTC
The ECT sensor temperature is less than -38°C (-36°F) for more than 10 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
| • | After starting the engine, the ECT should rise steadily, then stabilize when the thermostat opens. |
| • | A skewed sensor could result in poor driveability concerns. Refer to Temperature Versus Resistance . |
| • | If a malfunction is not present at this time, refer to DTC P1115 . |
| • | If an intermittent condition is suspected, refer to Intermittent Conditions . |
Test Description
The number below refers to the step number on the diagnostic table.
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 ECT sensor parameter less than the specified value? | -31°C (-24°F) | Go to Step 4 | Go to Step 3 | ||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||
Is the ECT sensor parameter more than the specified value? | 130°C (274°F) | Go to Step 8 | Go to Step 5 | |||||||||
5 |
Is the ECT sensor parameter more than the specified value? | 138°C (274°F) | Go to Step 7 | Go to Step 6 | ||||||||
6 | Test the signal circuit of the ECT sensor for the following conditions:
Repair the circuit as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 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: The sensor may be damaged if the circuit is shorted to a voltage source. Test for an intermittent and for a poor connection at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 12 | ||||||||
9 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
10 | 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 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 | ||||||||
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||
