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 Sensor Circuit Low Voltage
DTC P0118 00: Engine Coolant Temperature Sensor Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Signal | P0117 | P0118 | P0118 | --
Low Reference | -- | P0118 | -- | --

### Typical Scan Tool Data

#### ECT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: -39 to +142°C (-38 to +288°F) Varies with coolant temperature.
Signal | 149°C (300°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 V to the ECT signal circuit and supplies a ground to 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

• | The ignition is ON.

• | The engine speed is greater than 1 000 RPM.

### Conditions for Setting the DTC

#### P0117

The ECM detects the ECT voltage is below the threshold

#### P0118

The ECM detects the ECT voltage is above the threshold

### 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

• | 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 engine has sat overnight, the intake air temperature (IAT) sensor and the engine coolant temperature (ECT) sensor values should display within 3°C (5°F).

• | After starting a cold engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens.

• | High resistance in the circuits of either the ECT or IAT sensor may 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

1. Engine running for 60 s. Observe the DTC information with a scan tool. DTCs P0117 and P0118 should not set.
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 B34 Engine Coolant Temperature (ECT) Sensor.
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 is at -40°C (-40°F).

⇒ | If greater than the specified range, 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. Ignition ON, connect a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool ECT Sensor parameter is greater than 142°C (288°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 B34 Engine Coolant Temperature (ECT) Sensor.

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the harness connector at the B34 Engine Coolant Temperature (ECT) Sensor.
2. Test and record the resistance between the signal circuit terminal 2 and the low reference circuit terminal 1 at various ambient temperatures. Compare those measurements to the Temperature Versus Resistance table and verify that the resistance is within 5% of the specification.

⇒ | If not within the specified range, replace the B34 Engine Coolant Temperature (ECT) Sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Engine Coolant Temperature Sensor Replacement

• | Control Module References for engine control module replacement, setup, and programming