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	P0118¹	--
Low Reference	--	P0118	P0118¹	--
¹ 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	129°C (264°F), 0.0 Volts	-40°C (-40°F), 5.0 Volts	-40°C (-40°F), 5.0 Volts¹
Low Reference	--	-40°C (-40°F), 5.0 Volts	--
¹ 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

P0117 - Euro III Emissions

P0118 - Euro III Emissions

P0117 or P0118 - Euro IV Emissions

Conditions for Setting the DTC

P0117

The ECM detects that the ECT sensor is more than 149°C (300°F) for more than 4 seconds.

P0118

The ECM detects that the ECT sensor is less than -38°C (-34°F) for more than 6 seconds.

Action Taken When the DTC Sets

DTC P0117 and P0118 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTC P0117 and P0118 are Type B DTCs.

Diagnostic Aids

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Circuit/System Verification

1. Engine running, DTC P0117 and P0118 should not set.
2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

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 and ground.

⇒	If greater than 5 ohms, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

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

⇒	If greater than -40°C (-40°F), test the signal circuit of the ECT sensor for a short to ground. If the circuit tests normal, replace the ECM.

Important: If the signal circuit of the ECT sensor is shorted to voltage the ECT sensor may be damaged.

4. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit. Verify the ECT sensor parameter is greater than 128°C (262°F).

⇒	If less than 128°C (262°F), test the signal circuit of the ECT sensor for a short to voltage or an open/high resistance. If the circuit test 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 of 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 that the resistance is within 5 percent of the specification.

⇒	If the resistance vs temperature is not within 5 percent, replace the ECT sensor.

Repair Instructions