Circuit Description
The engine coolant temperature (ECT) sensor contains a thermistor which changes resistance based on temperature. The ECT sensor is located in the coolant crossover pipe at the center rear of the engine. The ECT sensor has a signal circuit and a ground circuit. The engine control module (ECM) applies a voltage, about 5.0 volts, on the signal circuit to the sensor. The ECM monitors any changes in this voltage caused by changes in the resistance of the sensor in order to determine the engine coolant temperature.
When the engine coolant is cold, the sensor resistance is high, and the ECM will sense a high signal voltage or low temperature. When the engine coolant is warm, the sensor resistance is low. This causes the ECM to sense a low signal voltage or high temperature.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The difference between the calculated engine coolant temperature and the actual engine coolant temperature is more than 12°C (22°F).
Action Taken When the DTC Sets
The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes. |
| • | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic. |
| • | The scan tool clears the MIL/DTC. |
Diagnostic Aids
Use the J 35616 connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector. Using this kit prevents damage to the harness or component terminals. Refer to Using Connector Test Adapters in Wiring Systems.
Check the following conditions:
| • | Poor connections at the ECM or at the component. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any of the related connectors and the wiring harnesses. A change in the display may help in order to locate the fault. |
| • | Check for a stuck open thermostat. A stuck thermostat, during very cold ambient conditions, may cause the engine temperature to increase too slowly and may set this DTC. |
| • | When checking the ECT sensor, the Temperature Versus Resistance - Engine Coolant Temperature Sensor table may be used in order to test the sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. |
| Refer to Symptoms for the Intermittents. |
| Important: The low reference for the ECT sensor is shared with the MAF sensor, CMP sensor, and the TP sensor. Do not use a test lamp to test the continuity of the low reference back through the ECM. Damage to the ECM will result. |
| • | If other DTCs are set that share the same ground circuit, test the point where the circuits splice and where the circuit connects to the ECM for opens or high resistance. |
If the engine has been allowed to sit overnight, the engine coolant temperature and the engine intake air temperature values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor to determine if the sensor is skewed.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
Is the ECT at the specified value? | -40°C (-40°F) | Go to Step 3 | Go to DTC P0115 Engine Coolant Temperature (ECT) Sensor Circuit | |
3 |
Is the ECT near the specified value? | 139°C (282°F) | Go to Step 4 | Go to DTC P0115 Engine Coolant Temperature (ECT) Sensor Circuit |
4 |
Was an engine cooling system repair made? | -- | Go to Step 6 | Go to Step 5 |
5 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 6 | -- |
6 |
Does the scan tool indicate that the diagnostic Passed? | -- | Go to Step 7 | Go to Step 2 |
7 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
