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CIRCUIT DESCRIPTION

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the signal circuit and a ground for the ECT low reference unit. When the ECT is low, the sensor resistance is high. When the ECT is high, the sensor resistance is low. The PCM uses this input for engine controls and enabling criteria for diagnostics. The internal clock of the PCM will record the amount of time the ignition is OFF. At restart the PCM will compare the temperature difference between the ECT and the intake air temperature (IAT). Before failing this test, the PCM will perform a calculation to determine the presence of a block heater. If the PCM detects that the temperature difference is not within the calibrated amount after the ignition OFF time, DTC P0116 sets.

CONDITIONS FOR RUNNING THE DTC

- The ignition is ON.
- DTCs P0112, P0113, P0117, P0118, P0125, P0128, P0601, P0602, P1621, P1683 are not set. The vehicle has a minimum ignition off time of 10 hours. The IAT sensor parameter is more than 15°C (59°F).

CONDITIONS FOR SETTING THE DTC

If the PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 15°C (27°F), the vehicle must be driven for more than 400 seconds over 24 km/h (15 mph). If the IAT sensor temperature decreases more than 3°C (5°F), a block heater is detected and the test is aborted. If the IAT sensor temperature does not decrease, a block heater was not detected and DTC P0116 sets.

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 a ECT sensor that is skewed high.
- An IAT sensor that is skewed low could cause this DTC to set.
- When testing the ECT sensor or the IAT sensor, the Temperature vs Resistance table should be used to determine if a skewed sensor is the problem. Refer to Temperature vs Resistance.

TEST DESCRIPTION

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
 
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