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 | High Resistance | Open | Short to Voltage | Signal Performance |
|---|---|---|---|---|---|
ECT Sensor Signal | P0117 | P0118 | P0118 | P0118 | P0116, P0125, P0128 |
Low Reference | -- | P0118 | P0118 | P0118, P0651 | P0125, P0128 |
Typical Scan Tool Data
Circuit | Normal Range | Short to Ground | Open | Short to Voltage |
|---|---|---|---|---|
ECT Sensor Signal | -39 to +120°C (-38 to +248°F) | 150°C (302°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 volts to the ECT sensor signal circuit and supplies a ground to the low reference circuit.
Conditions for Running the DTC
P0117
| • | The engine is running for more than 10 seconds. |
| OR |
| • | The engine run time is less than 10 seconds when the intake air temperature (IAT) is less than 50°C (122°F). |
| • | This DTC runs continuously within the enabling conditions. |
P0118
| • | The engine is running for more than 10 seconds. |
| OR |
| • | The IAT is more than 0°C (32°F). |
| • | This DTC runs continuously within the enabling conditions. |
Conditions for Setting the DTC
P0117
The ECM detects that the ECT is more than 149°C (300°F) for more than 5 seconds.
P0118
The ECM detects that the ECT is less than -39°C (-38°F) for more than 5 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
| • | If an engine overheating condition exists, it is possible to set a DTC P0117. Verify the proper heat range and the operation of the thermostat. Refer to Thermostat Diagnosis . |
| • | An ECT sensor signal circuit or low reference circuit that is shorted to another 5-volt reference circuit can cause a DTC P0118 to set. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
DTC Type Reference
Scan Tool Reference
Circuit/System Verification
- Turn OFF the ignition.
- Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
- Ignition ON, observe the ECT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.
- Use the scan tool to verify the proper operation of the engine cooling system fans.
- 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. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.
Circuit/System Testing
Important: All electrical components and accessories must be turned OFF and allowed to power down.
- Ignition OFF, disconnect the ECT harness connector at the ECT sensor.
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal Band ground.
- Ignition ON, verify the scan tool ECT Sensor parameter is less than -39°C (-38°F).
- Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B Verify the scan tool ECT Sensor parameter is greater than 149°C (300°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 terminal A for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | 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
Measure and record the resistance of the ECT sensor at various ambient temperatures, and then compare those measurements to the Temperature vs Resistance Table. Refer to Temperature Versus Resistance .
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
