P0118: Engine Coolant Temperature Sensor 1 Circuit High
The coolant temperature sensor voltage is too high, so the computer thinks the engine is extremely cold, even after warming up.
What P0118 means
P0118 is the high voltage version of the coolant sensor circuit code. The signal is stuck near the top of its range, around 4.5 to 5 volts, which the computer reads as an extremely cold engine. Often the scan tool will show about minus 40 degrees, the classic sign of an open circuit. KBB explains that this code can push the car into a failsafe mode, and that driving for long in that mode adds stress to engine parts. To be safe, many computers run the fans constantly and use a fixed fuel map, which can mean rich running, poor mileage and black smoke. The usual causes are an unplugged or loose connector, a broken wire, a corroded terminal or a failed sensor. RepairPal also mentions rusty coolant as a contributor. A shop checks the reading, then jumps the connector pins together; if the reading swings to very hot, the wiring is good and the sensor is bad. The repair is usually quick and inexpensive.
Common symptoms
- Check engine light on
- Poor gas mileage from extra fuel
- Black smoke or fuel smell
- Cooling fans may run all the time as a failsafe
- Temperature gauge reads cold or does not move
Most common causes
- ECT sensor unplugged or connector loose
- Open circuit in the sensor wiring
- Failed ECT sensor
- Corroded connector terminals
- Bad ground at the sensor
What to check yourself first
Check that the ECT sensor connector is fully plugged in, especially after recent cooling system work. A scan tool reading of about minus 40 degrees F on a warm engine means the computer sees an open circuit. Inspect the wiring for breaks.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace engine coolant temperature sensor | $499-$585 | When the sensor reads open with good wiring. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For a broken wire, loose connector or bad ground. |
| Coolant drain and refill | $440-$512 | If coolant is rusty or overdue and corroding the sensor. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0117 Engine Coolant Temperature Sensor 1 Circuit Low
- P0115 Engine Coolant Temperature Sensor 1 Circuit
- P0116 Engine Coolant Temperature Sensor 1 Circuit Range/Performance
- P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- P0113 Intake Air Temperature Sensor 1 Circuit High