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 Descriptors

DTC P0117: Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
DTC P0118: Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

### 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

### Typical Scan Tool Data

#### ECT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: -39 to +128°C (-38 to +262°F) Varies with coolant temperature.
ECT Sensor Signal | 129°C (264°F) | -40°C (-40°F) | -40°C (-40°F)*
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)*
* Internal ECM or ECT sensor damage may occur if the circuit is shorted to B+

### 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 signal circuit and supplies 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

• | The ignition is ON or the engine is running for greater than 2 seconds.

• | The DTCs run continuously once the above condition is met.

### Conditions for Setting the DTC

#### P0117

The ECM detects that the ECT is greater than 128°C (262°F).

#### P0118

The ECM detects that the ECT is less than -8°C (-36°F).

### Action Taken When the DTC Sets

DTC P0117 and P0118 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P0117 and P0118 are Type B DTCs.

### Diagnostic Aids

• | Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a DTC or a driveability condition. Refer to Temperature Versus Resistance .

• | If the vehicle has sat overnight, the IAT sensor and the ECT sensor values should display within 3°C (5°F).

• | After starting a cold engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens.

• | High resistance in the circuits of either the ECT or IAT sensor could set a DTC.

### 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. Engine running for 1 minute, observe the DTC information with a scan tool. DTCs P0117 and P0118 should not set.
2. 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, and the MAIN fuse removed, disconnect the harness connector at the ECT sensor.

Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.

Important: The control module or the sensor may be damaged if the circuit is shorted to battery positive voltage.

2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal 2 and ground.

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

3. Install the MAIN fuse. Ignition ON, verify the scan tool ECT sensor parameter is at -40°C (-40°F).

⇒ | If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.

4. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool ECT sensor parameter is greater than 128°C (262°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 or replace the ECT sensor.

### Component Testing

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

Important: A thermometer can be 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 engine control module replacement, setup, and programming