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 Repair Verification 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 | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118 | P0116, P0125, P0128
Low Reference | -- | P0118 | P0118 | P0118, P0651 | P0125, 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 | 150°C (302°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.

### Conditions for Running the DTC

#### P0117

• | The engine is running for more than 10 seconds.

| OR

• | The intake air temperature (IAT) is less than 50°C (122°F).

• | The DTCs run continuously when the conditions are met.

#### P0118

• | The engine running time is more than 10 seconds.

• | The intake air temperature is more than 0°C (32°F).

• | The DTCs runs continuously when the conditions are met.

### Conditions for Setting the DTC

#### P0117

• | The ECM detects that the resistance of ECT sensor is less than 45 ohms, approximately 150°C (302°F).

• | It occurs 5 times during the 6 tests.

• | DTC P0117 sets when the above conditions are met.

#### P0118

• | The ECM detects that the resistance of the ECT sensor is more than 450,000 ohms, about -60°C (-76°F).

• | It occurs 5 times during the 6 tests.

• | DTC P0118 is set when the above conditions are met.

### Action Taken When the DTC Sets

DTCs P0117 and P0118 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0117 and P0118 are Type B DTCs.

### Diagnostic Aids

• | If the engine exists overheated conditions, DTC P0117 may set and verify the proper heat range and the operation of the thermostat. Refer to Thermostat Diagnosis .

• | An ECT sensor signal circuit or low reference circuit that is shorted to another 5-volt reference circuit can cause a DTC P0118 to be set.

### 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

Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Engine Control Module Scan Tool Information

### Circuit/System Verification

Caution: 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 .
3. Ignition ON, observe the ECT sensor parameter. The reading should be -39 to +120°C (-38 to +248°F, according to the current ambient temperature and the vehicle operating conditions.
4. Use the scan tool to verify the proper operation of the engine cooling system fans.

### Circuit/System Testing

Important: 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 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