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, 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.

### Conditions for Running the DTC

#### P0117

• | The ignition is ON.

| OR

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

| OR

• | The engine run time is less than 10 seconds when the intake air temperature (IAT) is colder than 50°C (122°F).

• | This DTC runs continuously within the enabling conditions.

#### P0118

• | The ignition is ON.

| OR

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

| OR

• | The engine run time is less than 10 seconds when the IAT is warmer than 0°C (32°F).

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P0117

The ECM detects that the ECT is warmer than 149°C (300°F) for greater than 5 seconds.

#### P0118

The ECM detects that the ECT is colder than -39°C (-38°F) for greater 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.

### 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 ECT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F).
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, 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