P0118 - Engine Coolant Temperature Sensor 1 Circuit High
P0118 is a generic powertrain diagnostic trouble code indicating Engine Coolant Temperature Sensor 1 Circuit High. It relates to the Fuel & Air Metering system.
DTC Breakdown (SAE J2012)
| System | Powertrain (P) |
| Type | Generic |
| Subsystem | Fuel & Air Metering |
| Fault Index | 18 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code P0118 mean?
The engine control module logged P0118 after detecting an Engine Coolant Temperature (ECT) sensor high voltage fault.
Severity Level & Driveability Details
Severity: Moderate to High
If the ECT sensor reports incorrect low temperatures, the engine may overheat without the driver knowing, leading to head gasket failure.
Common Symptoms of P0118
- Check engine light illuminated.
- Engine cooling fans running constantly at high speed.
- Incorrect or erratic readings on the temperature gauge.
- Poor engine starting performance.
Typical Causes for P0118
- Failed Engine Coolant Temperature (ECT) sensor.
- Corroded connector terminals or damaged wiring for the sensor.
- Low coolant level or air pocket in the cooling system.
- Faulty engine thermostat.
Diagnostic and Troubleshooting Steps
Verify coolant level and check for leaks first. Monitor live ECT readings on a scan tool. If readings are stuck at extreme limits, test sensor resistance and reference voltage with a multimeter.
Typical Repairs and Fixes
- Replacing the Engine Coolant Temperature (ECT) sensor.
- Repairing connector wiring damage on the sensor harness.
- Topping off and bleeding air from the cooling system.
- Replacing the thermostat if stuck open.
Sensor Location & Parts Involved
The ECT sensor is screwed into the engine block or thermostat housing, contacting the engine coolant.
Clearing Code & Recurrence
Clear the code with an OBD2 scanner to verify that the temperature gauge rises smoothly.
Emissions & Smog Inspection Impact
Causes incorrect fuel mapping, increasing tailpipe emissions.
Free Check Engine Code Cheat Sheet (PDF)
Got your answer? Keep the top 50 most common diagnostic codes, their meanings, severity levels, and quick fixes handy in your vehicle's glovebox.
Related Diagnostic Codes
Sources & References
This diagnostic guide is compiled and verified against the following authority sources:
- NHTSA Safety Bulletins
- EPA OBD reference
Frequently Asked Questions about P0118
What does the ECT sensor circuit high input code P0118 mean?
The engine control module logged P0118 after detecting an Engine Coolant Temperature (ECT) sensor high voltage fault.
Is it safe to drive with the ECT sensor circuit high input code P0118 active?
Yes, but pay close attention to engine temperature.
How much does it cost to repair a ECT sensor circuit high input code P0118 fault?
The ECT sensor is $20-$50. Replacing the sensor with labor runs $100-$250.
What are the common causes of the ECT sensor circuit high input code P0118?
Trigger conditions for the ECT sensor circuit high input code P0118 include: Failed Engine Coolant Temperature (ECT) sensor., Corroded connector terminals or damaged wiring for the sensor., Low coolant level or air pocket in the cooling system..
Can I clear the check engine light for ECT sensor circuit high input code P0118?
Clear the code with an OBD2 scanner to verify that the temperature gauge rises smoothly.
Will the ECT sensor circuit high input code P0118 cause an inspection failure?
Causes incorrect fuel mapping, increasing tailpipe emissions.