P0118
DTC P0117 or P0118
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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 Voltage
DTC P0118
- Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
Diagnostic Fault Information
Typical Scan Tool Data
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 ignition is ON.
OR
* The engine is running for greater 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 ignition is ON.
OR
* The engine is running for greater than 10 seconds.
OR
* The engine run time is less than 10 seconds when the IAT is greater 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 greater than 149°C (300°F) for greater than 5 seconds.
P0118
The ECM detects that the ECT is less than -39°C (-38°F) for greater than 5 seconds.
Action Taken When the DTC Sets
DTCs P0117 and P0118 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs 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. Component Tests and General Diagnostics
* 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.
Circuit/System Verification
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.
1. Turn OFF the ignition.
2. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling (GE 47716 Fill) Cooling System Draining and Filling (Static Fill). Component Tests and General Diagnostics Service and Repair
3. 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.
4. Use the scan tool to verify the proper operation of the engine cooling system fans.
Circuit/System Testing
Important: All electrical components and accessories must be turned OFF and allowed to power down.
1. Ignition OFF, disconnect the ECT harness connector at the ECT sensor.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal A 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 less than -39°C (-38°F).
• If greater than the specified range, test the signal circuit terminal B 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 B and the low reference circuit terminal A. Verify the scan tool ECT Sensor parameter is greater than 149°C (300°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 the circuits test normal, test the ECT sensor.
Component Testing
Measure and record the resistance of the ECT sensor at various ambient temperatures, 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. Verification Tests
* Engine Coolant Temperature Sensor Replacement
* Control Module References for ECM replacement, setup, and programming Programming and Relearning