P0116

CIRCUIT DESCRIPTION
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. When the engine coolant temperatures are low, the resistance of the sensor is high. When the engine coolant temperatures are high, the resistance of the sensor is low. The ECT sensor has a signal circuit and a low reference circuit. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground tot he ECT low reference circuit. The ECM uses the following sensor inputs to calculate a predicted engine coolant temperature:
- The ECT sensor
- The intake air temperature (IAT)
- The mass air flow (MAF) sensor
- The engine speed (RPM)

The ECM compares the actual engine coolant temperature to a predicted engine coolant temperature. If the ECM detects that the actual engine coolant temperature is more than the predicted engine coolant temperature, DTC P0116 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0112, P0113, P0117, P0118, P0125, P0128, P0601, P0602, P0603, P0604, P0606 are not set.
- The engine run time is more than 8 minutes.
- The engine speed is more than 400 RPM.
- The accumulated MAF value is equal to a calculated value.

CONDITIONS FOR SETTING THE DTC
The ECM detects a temperature difference of more than 20°C (36°F) between the actual engine coolant temperature and the predicted engine coolant temperature.

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
- DTC P0116 is designed to detect an ECT sensor that is skewed high.
- An IAT sensor that is skewed low could cause this DTC to set.
- When inspecting the ECT sensor, the Temperature vs Resistance table should be used in order to determine if a skewed sensor is the concern.

TEST DESCRIPTION

Steps 1-3:

Steps 4-7:

Steps 8-12:

The numbers below refer to the step numbers on the diagnostic table.
3. This step tests for excessive resistance in the ECT sensor circuit.
4. This step tests for excessive resistance in the IAT sensor circuit.
8. This step tests for a skewed sensor through the range of temperatures affecting this DTC.