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 | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
ECT Sensor Signal | P0117 | P0118 | P0118* | P0116
Low Reference | -- | P0118 | P0118* | P0116
* ECM or sensor damage may occur if the circuit is shorted to B+.

### Typical Scan Tool Data

#### ECT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Varies with ambient 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)*
* ECM or sensor damage may occur if the circuit is shorted to B+.

### Circuit Description

This diagnostic determines if the ECT sensor 1 is biased warmer than normal. The ECM will record the amount of time the engine is OFF. If the required engine OFF time is met at start-up, the ECM compares the temperature difference between the ECT and the IAT sensor. If the ECM detects that the temperature difference is greater than a calibrated amount, the ECM sets the DTC.

The engine coolant temperature (ECT) sensor 1 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 a ground to the low reference circuit.

The following table illustrates the difference between temperature, resistance, and voltage:

ECT | ECT Resistance | ECT Signal Voltage
--- | --- | ---
Cold | High | High
Warm | Low | Low

### Conditions for Running the DTC

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

• | The ignition has been off for greater than 8 hours before the engine is started.

• | The engine is running.

• | The intake air temperature (IAT) is greater than -7°C (19°F).

• | The engine block heater (if equipped) is not detected.

• | The DTC runs once per cold start when the above conditions are met.

### Conditions for Setting the DTC

• | The ECM detects a temperature difference on a cold start-up that indicates that the ECT sensor is 20°C (36°F) greater than the IAT sensor.

| OR

• | The ECM detects a temperature difference on a cold start-up that indicates that the ECT sensor is 20°C (36°F) greater than the IAT sensor, and the time spent cranking the engine is greater than 10 seconds without starting, if the ECM does not detect the fuel level is low.

### 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.

• | An IAT sensor that is biased 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.

• | Test the ECT sensor at various temperature levels in order to evaluate the possibility of a biased sensor. A sensor that is biased warmer can result in a driveability condition. Refer to Temperature Versus Resistance.

• | If the condition is intermittent, allowing the vehicle to sit for greater than 8 hours with the ignition OFF, may help isolate the condition. Compare the scan tool RCT and ECT temperature sensor values at Ignition ON. The RCT sensor and the ECT sensor values should display within 3°C (5°F).

### 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 ON, observe the DTC information with a scan tool. Verify that DTC P0112, P0113, P0117, or P0118 is not set.

⇒ | If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Loss of Coolant and Cooling System Draining and Filling.
3. Inspect the thermostatically-controlled coolant heater, if equipped, for damage or modifications. Test for the correct operation of the coolant heater. Refer to Coolant Heater Inoperative.
4. Engine idling for 15 minutes with the A/C OFF.

Note: Depending on ambient temperature, it may take up to 4 minutes for the temperatures to equalize.

5. Command the Engine Coolant Thermostat Heater to 100 percent with a scan tool. Increase the engine speed to 3,000 RPM. Observe the scan tool RCT and the ECT sensor parameters. The RCT and the ECT sensor parameters should be within 20°C (68°F).
6. 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 1.
2. Ignition OFF for 1 minute, test for less than 5 Ω between the low reference circuit terminal 1 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 at -40°C (-40°F).

⇒ | If warmer than the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the ECM.

Note: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

4. Install a 1 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool ECT sensor parameter is greater than 149°C (300°F).

⇒ | If less than 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 or replace the ECT sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the ECT sensor.

Note: A thermometer can be used to the used to test the sensor off the vehicle.

2. Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.

⇒ | If not within the specified range, replace the ECT sensor.

### 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