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 | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118* | P0116, P0125, P0128
Low Reference | -- | P0118 | P0118 | P0118* | P0125, P0128
*ECM or sensor damage may occur if the circuit is shorted to B+

### Typical Scan Tool Data

#### ECT Sensor Temperature

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop 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 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 ignition is ON when the intake air temperature (IAT) is less than 50°C (122°F).

• | This DTC runs continuously when the above conditions are met.

#### P0118

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

| OR

• | The ignition is ON when the IAT is more than 0°C (32°F).

• | This DTC runs continuously when the above conditions are met.

### Conditions for Setting the DTC

#### P0117

The ECM detects that the ECT is more than 150°C (302°F) for more than 5 seconds.

#### P0118

The ECM detects that the ECT is less than -60°C (-76°F) for more than 5 seconds.

### Action Taken When the DTC Sets

DTCs P0117 and P0118 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs 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 and 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

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.
3. Turn ON the ignition, with the engine OFF.
4. Use the scan tool to verify the proper operation of the engine cooling system fans.
5. Turn OFF the ignition.
6. Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis.

### Circuit/System Testing

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