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

#### ECT Sensor Temperature

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running Parameter Normal Range: -39 to +120°C (-38 to +248°F)
ECT Sensor Signal | 150°C (302°F) | -40°C (-40°F) | -40°C (-40°F)
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)

### Circuit/System 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 diagnostic to determine if the input from the ECT sensor is skewed warmer than normal. 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, 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.

### Conditions for Running the DTC

• | DTCs P0112, P0113, P0117, P0118, P0128, P0502, P0503, P0601, P1621, P2610 are not set.

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

• | The ignition is ON.

• | The start-up IAT is greater than -7°C (+19°F).

• | The Fuel Level Sensor parameter is greater than 2.5 percent.

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

### Conditions for Setting the DTC

• | The ECM detects a temperature difference at power-up that indicates that the ECT sensor is 30°C (54°F) greater than the IAT sensor.

| OR

• | The ECM detects a temperature difference at power-up that indicates that the ECT sensor is 16°C (29°F) greater than the IAT sensor, and the time spent cranking the engine is greater than 30 seconds when the fuel level is greater than 2.5 percent.

| OR

• | The ECM detects a temperature difference at power-up that indicates that the ECT sensor is 16°C (29°F) greater than the IAT sensor. Then the vehicle must be driven for greater than 6 minutes and 40 seconds at greater than 24 km/h (15 mph). If the IAT sensor then decreases greater than 5°C (9°F), an engine block heater was detected and the test is aborted. If the IAT sensor does not decrease, an engine block heater was not detected and DTC P0116 will set.

### Action Taken When the DTC Sets

DTC P0116 is a Type B DTC.

### Conditions for Clearing the MIL/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 a high resistance short to ground. This condition results in less voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a warmer ECT.

• | This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures greater than -8°C (+18°F), then compare those measurements to the Temperature vs Resistance table. 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 to 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

• | Engine Controls Connector End Views

• | Engine Control Module Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Verification

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.

1. Turn OFF the ignition.
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 .

Important: Determine the ambient temperature by using an accurate thermometer.

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

### Circuit/System Testing

1. Ignition OFF, disconnect the ECT harness connector at the ECT sensor.
2. Ignition OFF for 90 seconds, 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 ECM.

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

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 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 tests normal, replace the ECM.

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

### Component Testing

Measure and record the resistance of the ECT sensor at various ambient temperatures, then compare those measurements to 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