OBD-II · Engine and powertrain (P)
P0118
Engine coolant temperature circuit high input
What it means
The coolant temperature signal voltage is above its valid range, which the ECU would read as an extremely cold engine. This is usually an open circuit or unplugged sensor.
Symptoms
- cooling fan running all the time
- wrong or no temperature gauge reading
- hard starting, rough running or higher fuel consumption
- engine warning light
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | open circuit |
| 02 | unplugged sensor |
| 03 | failed sensor |
| 04 | poor ground |
| 05 | broken terminal |
What to check, step by step
- 01Check the coolant level first
- 02Compare the coolant temperature in live data with outside air temperature after an overnight cold soak, then with the real warm engine temperature
- 03Inspect the sensor connector for corrosion and broken locking tabs
- 04Measure the sensor resistance against temperature and check the wiring to the ECU
- 05Replace the sensor (usually cheap) and bleed the cooling system afterwards