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 Descriptor

DTC P0117 00: Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
DTC P0118 00: 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 00 | P0118 00 | P0118 00* | --
Low reference | -- | P0118 00 | P0118 00* | --
* Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### Typical Scan Tool Data

#### ECT Sensor 1

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in closed loop Parameter Normal Range: Varies with ambient air temperature, within a range of -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)*
* Internal ECM or sensor damage may occur if the circuit is shorted to B+.

### Circuit/System Description

The engine coolant temperature (ECT) sensor 1 is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 V to the engine coolant temperature (ECT) sensor 1 signal circuit and a ground for 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

#### P0117 00

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

• | The battery voltage is greater than 9 V.

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

#### P0118 00

• | The engine run time is greater than 60 s.

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

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

### Conditions for Setting the DTC

#### P0117 00

The ECM detects that the engine coolant temperature (ECT) sensor 1 signal is less than 0.27 V, which is warmer than 137°C (279°F) for greater than 2 s.

#### P0118 00

The ECM detects that the engine coolant temperature (ECT) sensor 1 signal is greater than 4.96 V, which is colder than -39°C (-38°F) for greater than 2 s.

### Action Taken When the DTC Sets

• | DTCs P0117 00, and P0118 00 are Type B DTCs

• | The cooling fans will be commanded ON.

• | The A/C compressor will be commanded OFF.

### Conditions for Clearing the DTC

DTCs P0117 00, and P0118 00 are Type B DTCs

### Diagnostic Aids

Note: The engine coolant temperature (ECT) sensor 1 is mounted on the engine and the engine coolant temperature (ECT) sensor 2 (radiator coolant temperature (RCT) sensor) is mounted on the radiator.

• | The engine coolant temperature gage will display full cold when an ECT DTC sets.

• | After starting the engine, the engine coolant temperature (ECT) sensor 1 temperature should rise steadily, then stabilize after the thermostat opens.

• | Test the engine coolant temperature (ECT) sensor 1 at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition.

### 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. If the ignition has been OFF for 8 h or greater, the intake air temperature, ambient air temperature, and the engine coolant temperature (ECT) sensor 1 should be within 9°C (16°F) of each other. Ignition ON, observe the scan tool IAT Sensor, Ambient Air Temperature, and the ECT Sensor 1 parameters. Compare those sensor parameters to each other to determine if the condition is current.
2. Engine running, observe the ECT Sensor 1 parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient air temperature, the engine run time, and the vehicle operating conditions.
3. 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 B34A Engine Coolant Temperature (ECT) Sensor 1.
2. Ignition OFF, test for less than 5 Ω between the low reference circuit terminal 2 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 K20 Engine Control Module (ECM).

3. Ignition ON, verify the scan tool ECT Sensor 1 is at -40°C (-40°F).

⇒ | If warmer than the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module (ECM).

Note: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

4. Install a 3 A fused jumper wire between the engine coolant temperature (ECT) sensor 1 signal circuit terminal 1 and ground. Verify the scan tool ECT Sensor 1 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 K20 Engine Control Module (ECM).

5. If all circuits test normal, test or replace the B34A Engine Coolant Temperature (ECT) Sensor 1.

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the harness connector at the B34A Engine Coolant Temperature (ECT) Sensor 1.
2. Test the B34A Engine Coolant Temperature (ECT) Sensor 1 by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the LINK (Temperature Versus Resistance) table and verify that the resistance is within 5% of the specification.

⇒ | If not within the specified range, replace the B34A Engine Coolant Temperature (ECT) Sensor 1.

### 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