The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit.

The ECM uses this high side coolant rationality diagnostic to determine if the input from the ECT sensor is skewed high. The internal clock of the ECM will record the amount of time the ignition is OFF. If the calibrated ignition OFF time is met at start-up, then the ECM will compare the temperature difference between the ECT and the intake air temperature (IAT) to determine if the temperatures are within an acceptable operating range of each other. This DTC will only run once during the ignition cycle within the enabling conditions. If the ECM detects that the temperature difference is not within the calibrated range after the ignition OFF time, DTC P0116 will set.

DTC P0116 are type B DTC.

DTC P0116 are type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References

1. If the ignition has been OFF for 8 hours or more the ECT and the IAT should be within 6°C (11°F) of each other and also the ambient temperature. Ignition ON, with the engine OFF and use a scan tool to observe the IAT and the ECT sensor parameters. Compare those sensor parameters to each other and also to the ambient temperature. A slight to moderate resistance in the IAT signal or low reference circuit can widen the spread between the two sensors and cause this DTC to set.
2. An IAT sensor that is skewed lower at various ambient temperatures due to more resistance than is normal can widen the spread between the two sensors and cause this DTC to set. Measure and record the resistance of the IAT sensor at various ambient temperatures and then compare those measurements to the Temperature Versus Resistance Table. Refer to Temperature Versus Resistance .
3. Inspect the ECT sensor terminals for corrosion and for engine coolant leaking through the sensor.

Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.

4. Ignition OFF.
5. Inspect the cooling system for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .

1. Disconnect the ECT sensor.
2. Ignition ON, engine OFF.
3. Measure for the proper range of 4.9-5.2 volts between the ECT sensor signal circuit and a known ground with a DMM.

⇒	If the voltage is less than 4.9 volts, test the ECT sensor signal circuit for a short to ground or an open/high resistance.

⇒	If the ECT sensor signal circuit tests normal and the voltage is still not within the proper range then replace the ECM.

4. Remove and test the ECT sensor. Refer to Component Testing.

⇒	If the resistance measurements of the ECT sensor are out of range, replace the sensor.

⇒	If the ECT sensor tests normal and the DTC continues to set then replace the ECM.

Measure and record the resistance of the ECT sensor at various ambient temperatures, and then compare those measurements to the Temperature Versus Resistance Table. Refer to Temperature Versus Resistance .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.