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
DTC P0119: Engine Coolant Temperature (ECT) Sensor Circuit Intermittent

### 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, P0119
Low Reference | -- | P0118 | P0118 | P0118 | P0125, P0128, P0119

### Typical Scan Tool Data

#### ECT Sensor Temperature

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running Parameter Normal Range: -39 to +120°C (-38 to +248°F)
ECT Sensor Signal | 143°C (289°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 supplies a ground to the low reference circuit.

### Conditions for Running the DTC

#### P0117

• | The ignition is ON or the engine is running.

• | This DTC runs continuously within the enabling conditions.

#### P0118

• | The ignition is ON or the engine is running.

• | This DTC runs continuously within the enabling conditions.

#### P0119

• | The ignition is ON or the engine is running.

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P0117

The ECM detects that the ECT is greater than 140°C (284°F) for greater than 4 seconds.

#### P0118

The ECM detects that the ECT is less than -39°C (-38°F) for greater than 4 seconds.

#### P0119

The ECM detects that the ECT sensor signal is intermittent or has abruptly changed for greater than 4 seconds.

### Action Taken When the DTC Sets

DTCs P0117, P0118 and P0119 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0117, P0118 and P0119 are Type B DTCs.

### Diagnostic Aids

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

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### 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. If the ignition has been OFF for 8 hours or greater, the intake air temperature (IAT), the IAT 2 and the ECT should be within 9°C (16°F) of each other and also the ambient temperature. Ignition ON, observe the scan tool IAT Sensor, IAT 2 Sensor and the ECT Sensor parameters. Compare those sensor parameters to each other and also to the ambient temperature to determine if the condition is current.
4. Engine running, observe the ECT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.
5. Use the scan tool to verify the proper operation of the engine cooling system fan.

### Circuit/System Testing

1. Ignition OFF, disconnect the ECT harness connector at the ECT sensor.
2. Ignition OFF for 90 seconds , test for less than 5 ohms of resistance between the low reference circuit 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 less than -39°C (-38°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. Install a 3A fused jumper wire between the signal circuit and the low reference circuit. Verify the scan tool ECT Sensor parameter is greater than 140°C (284°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 the circuits test normal, test 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