What P0118 means
The control module detected a coolant-temperature sensor circuit signal in a high range for the vehicle’s monitoring strategy. The code does not by itself prove the sensor, wiring, connector, or engine temperature is the cause.
A trouble code identifies a detected condition. Use the surrounding evidence to choose a test instead of treating the code as a failed-part diagnosis.
- 01PreserveCode, module, freeze frame, readiness
- 02ClassifyEngine Coolant Temperature Sensor 1 Circuit High
- 03InspectCoolant-temperature sensor or connector concern / Open, short, high-resistance, or damaged wiring
- 04TestLet the engine cool before checking the cooling system or connector / Preserve freeze-frame data and compare reported temperature with ambient when fully cold
- 05VerifyRepair only when evidence supports it; retest
Follow the sequence, stop when evidence changes the path, and verify the exact vehicle information before acting.
Record every stored and pending code, freeze frame, readiness state, and relevant live data before clearing anything. Companion codes and operating conditions often matter more than the code name.
Symptoms you may notice
- Check-engine light
- Temperature reading may be implausible
- Hard starting or poor drivability
- Cooling-fan behavior may change
Cause groups to investigate
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Use codes, data, inspection, and controlled testing to decide whether this group is supported on the exact vehicle.
Diagnostic route
Let the engine cool before checking the cooling system or connector
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Preserve freeze-frame data and compare reported temperature with ambient when fully cold
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Inspect the sensor circuit and recent work using the exact wiring information
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Compare sensor signal and circuit evidence before replacing the sensor
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Verify plausible temperature behavior and monitor completion after the confirmed repair
Follow the vehicle’s exact test conditions, wiring, thresholds, and safety procedure. Record the result before moving to the next step.
Common mistakes
- Applying a universal voltage or resistance valueA diagnostic trouble code identifies a detected condition; it does not automatically identify the failed part.
- Opening a hot pressurized cooling systemA diagnostic trouble code identifies a detected condition; it does not automatically identify the failed part.
- Replacing the sensor without checking the harness and connectorA diagnostic trouble code identifies a detected condition; it does not automatically identify the failed part.
Sources and verification
The standardized code meaning is tied to SAE J2012. Additional government sources may document the monitor family or public code description. Cause groups and diagnosis remain general guidance; manufacturer-enhanced definitions, enable criteria, test values, and exact procedures require authoritative information for the vehicle.