Diagnostic Instructions

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	Open/High Resistance	Short to Voltage	Signal Performance
ECT Sensor Signal	P0117	P0118	P0118*	--
Low Reference	--	P0118	P0118**	--
* Sensor damage may occur if the circuit is shorted to B+. ** Internal ECM damage may occur if the circuit is shorted to B+.

Typical Scan Tool Data

ECT Sensor

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Engine operating in Closed Loop Parameter Normal Range: Varies with ambient temperature
ECT Sensor Signal	120°C (248°F), 0.0 Volts	-40°C (-40°F), 5.0 Volts	-40°C (-40°F), 5.0 Volts
Low Reference	-40°C (-40°F), 5.0 Volts	-40°C (-40°F), 5.0 Volts	-40°C (-40°F), 5.0 Volts*
* Internal ECM damage may occur if the circuit is shorted to B+.

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.

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

Conditions for Setting the DTC

P0117

The ECM detects that the ECT voltage is less than 0.03 volt.

P0118

The ECM detects that the ECT voltage is greater than 4.98 volts.

Action Taken When the DTC Sets

DTC P0117 and P0118 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTC P0117 and P0118 are Type A DTCs.

Diagnostic Aids

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions for scan tool information

Scan Tool Reference

Control Module References

Circuit/System Verification

1. Engine running for 1 minute, 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 ECT sensor.
2. Ignition OFF, test for less than 5 ohms of resistance 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 ECM.

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

⇒	If greater than the specified value, 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 terminal 1 and the low reference circuit terminal 2. Verify the scan tool ECT sensor parameter is greater than 120°C (248°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

1. Ignition OFF, disconnect the harness connector at the ECT sensor.

Important: A thermometer can be used to test the sensor off the vehicle.

2. Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify the resistance is within 5 percent of the specification.

⇒	If not within the specified range, replace the ECT sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.