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 provide 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

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine running at various operating conditions Parameter Normal Range: Varies with coolant temperature
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 a ground for 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

• | DTC P0112, P0113, P0117, P0118, P0128, P0502, P0503, P0601, P1621, or P2610 is not set.

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

• | The ignition is ON.

• | The start-up IAT is warmer 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) warmer 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) warmer 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) warmer 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

• | 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.

• | 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 Versus Resistance table.

• | 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

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling.
2. Ignition OFF for 8 hours or greater.
3. Ignition ON, observe the scan tool ECT Sensor and IAT Sensor parameters. The ECT, IAT, and ambient temperature should be within 15°C (27°F) of each other.
4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ECT sensor.
2. Ignition OFF, test for less than 5 ohms 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 colder than -39°C (-38°F).

⇒ | If warmer 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 warmer than 149°C (300°F).

⇒ | If colder 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 the circuits test normal, test or replace 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 Versus Resistance table.

### 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