For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0116: Engine Coolant Temperature (ECT) Sensor Performance

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118 | P0116, P0128
Low Reference | -- | P0118 | P0118 | P0118 | P0128

### Typical Scan Tool Data

#### Engine Coolant Sensor Temperature

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Parameter Normal Range: -39 to +120°C (-38 to +248°F)
ECT Sensor Signal | 151°C (303°F) | -40°C (-40°F) | -40°C (-40°F)
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)

### Circuit Description

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 sensor signal circuit and supplies a ground to the low reference circuit.

The ECM uses this high side coolant rationality diagnosis to determine if the output from the ECT sensor is skewed warmer than normal. The internal clock of the ECM will record the times of the ignition OFF. If the calibrated ignition OFF, time is met at start-up, the ECM will compare the difference between the ECT and the intake air temperature (IAT) to determine if the temperatures are within an acceptable operating range of each other.

### Conditions for Running the DTC

• | DTCs P0112, P0113, P0117, P0118, P0128, P0502, P0503, P0601, P2610 are not set.

• | The ECM has not been detected control module long term memory performance fault.

• | Engine internal OFF timer performance DTCs of the ECM is inactive.

• | The vehicle has had a minimum ignition OFF time of 8 hours.

• | With this ignition cycle runs, and test occurred fault.

• | With this ignition cycle breaks, and test occurred fault.

• | This DTC runs once per ignition cycle within the enabling conditions.

### Conditions for Setting the DTC

• | When the ECM is on after the engine continual stop at least 8 hours that detects that the ECT sensor is more than the IAT sensor.

• | When the ECM is On after the engine continual stop at least 8 hours that has not been detected engine block heater, when energized the ECT sensor is more than the IAT sensor 20°C (36°F); when energized the IAT sensor more than -7°C (+19.4°F); compared at least 15 km/h (9 mph) after 400 seconds to power, after the IAT value is down at least 4°C (7°F), when the ECM is power that detects that the ECT sensor is more than the IAT sensor 10°C (18°F).

• | After the engine continual stops for at least 8 hours and when the fuel level is more than 5 percent, the engine starting time is more than 5 minutes, detects that the ECT sensor is more than the IAT sensor 10° C (18°F), when the ECM is powered.

• | DTC P0116 is set when one of the above conditions occur.

### Action Taken When the DTC Sets

DTC P0116 is a Type B DTC.

### Conditions for Clearing the DTC

DTC P0116 is a Type B DTC.

### Diagnostic Aids

• | Inspect the ECT sensor terminals for corrosion and for engine coolant leaking through the sensor. Engine coolant that is leaking through the sensor will create high resistance, short to ground. This condition can result in lower voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a warmer ECT.

• | This diagnostic runs in a specific range. When it is more than -8°C (+18°F), refer to Temperature Versus Resistance.

• | An IAT sensor that is skewed colder at various ambient temperatures due to greater resistance than is normal will increase the range between these two sensors. Measure and record the resistance of the IAT sensor at various ambient temperatures, then compare those measurements with the Temperature vs Resistance table. Refer to Temperature Versus Resistance.

• | A slight to moderate resistance in the IAT sensor signal circuit or low reference circuit will increase the range between these two sensors. This condition results in a greater voltage on the IAT sensor signal circuit, which is interpreted by the ECM as a colder IAT.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Engine Control Module Scan Tool Information

#### Special Tools

J 38522 Variable Signal Generator

### Circuit/System Verification

Warning: To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot.

1. Turn the ignition OFF.
2. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling.

Note: Determine the ambient temperature with an accurate thermometer.

3. If the ignition has been OFF for 8 hours or more, the ECT and the IAT should be within 15°C (27°F) of each other and also the ambient temperature. Turn the ignition ON, observe the scan tool start-up ECT and start-up IAT sensor parameters. Compare those sensor parameters with each other and also with the ambient temperature to determine if the ECT sensor is skewed warmer.

### Circuit/System Testing

Note: All electrical components and accessories must be turned OFF and allowed to power down.

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

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

3. Ignition ON, verify the scan tool ECT sensor parameter is less than -39°C (-38°F).

⇒ | If more than the specified value, test the signal circuit terminal A for short to ground. If the circuit test normal, replace the ECM.

4. Connect a 3-amp fused jumper wire between the signal circuit terminal A and the 5-volt low reference circuit terminal B. Verify the ECT sensor parameter is greater than 149°C (300°F).

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

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

### Component Testing

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Engine Coolant Temperature Sensor Replacement

• | Control Module References for ECM replacement, setup, and programming