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.
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 P0118 Engine Coolant Temperature (ECT) Sensor Circuit High 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 less than -39°C (-38°F) for 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
| • | If a short to a separate 5-volt source occurs this DTC may set. If this is found to be the problem, a continuity test to all other PCM circuits will be necessary 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 to test the engine coolant temperature (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 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 numbers below refer to the step numbers on the diagnostic table.
-
This step isolates the condition. If the temperature changes, test for a condition in the low reference circuit. If the temperature remains the same test the signal circuit for a condition.
-
This step tests for the correct 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.
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? | -38°C (-36°F) | Go to Step 3 | Go to Step 4 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the temperature less than the specified value? | 138°C (280°F) | Go to Step 5 | Go to Step 6 |
Is the temperature more than the specified value? | 138°C (280°F) | Go to Step 7 | Go to Step 8 | |
Important: If the fuse in the jumper wire opens, repair the short to B+, and replace the sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did any additional DTCs set? | -- | Go to Step 11 | Go to Step 9 | |
7 | Test the low reference circuit of the ECT sensor for an open, or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
8 | Test the signal circuit of the ECT sensor for an open, or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
9 | Test for shorted terminals and for poor connections at the IAT 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 14 | Go to Step 12 |
10 | Test for shorted terminals and for poor connections 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 14 | Go to Step 13 |
11 | Repair the short between the signal circuit of the ECT sensor and the circuit for which the DTC set. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- |
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 |
15 | Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? | -- | System OK | |
