P0118 means Engine Coolant Temperature Sensor 1 Circuit High. The coolant temperature sensor signal is reading high voltage, which the computer interprets as a very cold engine or an open circuit. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0118 means
The coolant temperature reading feeds many systems: warm-up fueling, ignition timing, idle speed, cooling fan control, transmission shift timing and often the dash gauge. A wrong reading causes symptoms far beyond the cooling system, and a real overheat can damage an engine quickly. Confirm the actual temperature with a scan tool or an infrared thermometer before replacing parts.
P0118 symptoms
- Cooling fans running constantly as a precaution
- Rich running, black smoke or poor fuel economy
- Temperature gauge reading cold or not moving
Common causes of P0118
- Unplugged or broken connector
- Open circuit in the wiring
- Failed sensor
How to diagnose P0118
- Check the connector is fully seated
- Compare the scan tool reading with the actual engine temperature
- Check wiring continuity and sensor resistance
Can you drive with P0118?
Drivable in the short term, but watch the real temperature, since the gauge may not show overheating.
P0118 tips
The opposite of P0117: a reading of about -40 degrees on a warm engine is the classic sign of an open circuit, such as an unplugged connector or a broken wire. Many vehicles have a separate gauge sender, so the dash gauge can look normal while the computer sees the fault.
Will P0118 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0118 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0117 | Engine Coolant Temperature Sensor 1 Circuit Low |
| P0128 | Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) |
| P0172 | System Too Rich (Bank 1) |
Guides that help
When it is more than a sensor
Most cooling codes end with a thermostat, sensor, fan or leak repair. If the engine overheated badly enough to fail the head gasket or warp the heads, compare a repair against a replacement on our engines page and read engine replacement cost.
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