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 VoltageDTC 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 | P0115 |
Low Reference | -- | P0118 | P0118¹ | P0115 |
¹ Internal ECM damage may occur if the circuit is shorted to B+. | ||||
Typical Scan Tool Data
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 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
| • | The engine run time is greater than 2 minutes. |
| OR |
| • | The ignition has been off for more than 6 hours before the vehicle is started. |
| • | The DTC runs continuously when either of the above conditions are met. |
P0118
| • | The engine run time is greater than 2 minutes. |
| • | The intake air temperature (IAT) sensor is greater than -10°C (14°F). |
| • | The DTC runs continuously when the above conditions are met. |
Conditions for Setting the DTC
P0117
The ECM detects that the ECT sensor is more than 149°C (300°F).
P0118
The ECM detects that the ECT sensor is less than -38°C (-34°F).
Action Taken When the DTC Sets
| • | DTC P0117 and P0118 are Type A DTCs. |
| • | The cooling fans will be commanded ON by the ECM. |
Conditions for Clearing the MIL/DTC
DTC P0117 and P0118 are Type A DTCs.
Diagnostic Aids
| • | After starting the engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens. |
| • | 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 driveability condition. |
| • | If the vehicle has set overnight, the ECT sensor and the IAT sensor values should display within 3°C (5°F). |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Circuit/System Verification
- Engine running, DTC P0117 and P0118 should not set.
- 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 Data List.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the ECT sensor.
- Ignition ON, clear the DTC information with a scan tool.
- Ignition ON, verify that the ECT sensor parameter is at -40°C (-40°F).
- Test for less than 0.5 volt between the low reference circuit and ground.
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.
- Ignition ON, clear the DTC information with a scan tool.
- Install a 1-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 all circuits test normal, test or replace the ECT sensor.
| ⇒ | If greater than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified value, test the low reference circuit for a short to voltage. If the circuit/connections test normal, replace the ECM. |
| ⇒ | If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM. |
Important: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.
| ⇒ | If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector of the ECT sensor.
- 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.
Important: A thermometer can be used to the used to test the sensor off the vehicle.
| ⇒ | If the resistance vs temperature is not within 5 percent, replace the ECT sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for engine control module replacement, setup, and programming |
