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 | P0118* | P0116 |
Low Reference | -- | P0118 | P0118* | P0116 |
* Internal ECM or sensor 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 | 214°C (417°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 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 greater 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
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running, observe the DTC information with a scan tool. DTCs P0117 or P0118 should not set.
- 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
- Ignition OFF, disconnect the harness connector at the ECT sensor.
- Ignition ON, clear the DTC information with a scan tool.
- Ignition OFF, test for less than 5 ohms between the low reference circuit terminal B or 2 and ground.
- Ignition ON, verify the scan tool ECT sensor parameter is at -40°C (-40°F).
- Ignition ON, clear the DTC information with a scan tool.
- Install a 1A fused jumper wire between the signal circuit terminal A or 1 and the low reference circuit terminal B or 2. 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 range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests 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 range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
Component Testing
- Ignition OFF, disconnect the harness connector at 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 test the sensor off the vehicle.
| ⇒ | If not within the specified range, replace the ECT sensor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
