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 signal circuit and a ground for the low reference circuit. When the engine coolant temperatures are low, the resistance is high. When the engine coolant temperatures are high, the resistance is low. The ECM uses this high side coolant rationality test to determine if the ECT input is skewed. The ECM will record the amount of time the engine is OFF. At restart, the ECM will compare the temperature difference between the ECT and the intake air temperature (IAT) sensor 2.

The ECM detects that the difference of maximum ECT and minimum ECT is less than (1-15°C) for longer than 5 seconds.

DTC P0116 is a Type A DTC.

DTC P0116 is a Type A DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Important: The engine needs to have been OFF for at least 10 hours for the ECT and the IAT sensor 1 to be at ambient temperature. The vehicle should not have changed environments during this time.

1. If the ignition has been OFF for 10 hours or more, the ECT and the IAT sensor 2 should be within 6°C (11°F) of each other, and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the IAT sensor 2 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 2 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 2 at various ambient temperatures, then compare those measurements to the Temperature vs. 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. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .

1. Ignition OFF, disconnect the harness connector at the ECT sensor.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal A and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the control module.

3. Ignition ON, verify the scan tool ECT parameter is less than -40°C (-40°F).

⇒	If greater than the specified range, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the control module.

4. Install a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool ECT parameter is greater than 130°C (266°F)

⇒	If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.

5. If all circuits test normal, test or replace the ECT sensor.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.