P0115

Circuit Description
The Engine Coolant Temperature (ECT) sensor contains a device which changes the resistance that is based on temperature (a thermistor). 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 ECM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The ECM monitors the changes in this voltage that are caused by the changes in the resistance of the sensor in order to determine the Engine Coolant Temperature.

When the engine coolant is cold, the sensor (thermistor) resistance is high. Therefore, the ECM will sense a high signal voltage (low temperature). When the engine coolant is warm, the sensor resistance is low. This causes the ECM to sense a low signal voltage (high temperature).

When the ECM senses a signal voltage outside of the normal operating range of the sensor, this DTC will set.

Conditions for Running the DTC
The engine must be running.

Conditions for Setting the DTC
^ The ECT signal voltage indicates an ECT that is more than 139°C (282°F).
OR
^ The ECT signal voltage indicates an ECT that is at -40°C (-40°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 ECM battery voltage is interrupted.
^ The scan tool clears the MIL/DTC.

Diagnostic Aids

Notice: Refer to J 35616-A Connector Test Adapter Kit Notice in Service Precautions.

Use the J 35616-A Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

Check the following conditions:
^ Poor connections at the ECM or at the component-Inspect the harness connectors for the following:
- Improper mating Broken locks
- Poor terminal to wire connection
^ If the sensor signal is only affected when the harness is moved at a component, and there is no problem with the harness or the connections, the component may be damaged.
^ When checking the ECT sensor, the Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor may be used in order to test the sensor at various temperature levels in order to evaluate the possibility of a shifted sensor. A shifted sensor could result in poor driveability complaints. Refer to Symptoms, Preliminary Checks, for the intermittents.
^ If other DTCs are set that share the same ground circuit, check the point where the circuits ground to the chassis or the engine block. 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 the Temperature vs Resistance - Intake Air Temperature (IAT) Sensor. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Turn ON the engine and monitor the ECT. The temperature should rise steadily with the ECT sensor temperature.
5. Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same Freeze Frame conditions (the RPM, the MAF, the vehicle speed, the temperature, etc.) that were noted. This process may help to recreate the malfunction.
19. Perform the Idle Learn Procedure when replacing the ECM or throttle body.