OBD-II · Engine and powertrain (P)
P0115
Engine coolant temperature circuit fault
What it means
The coolant temperature sensor circuit signal is invalid or unavailable. Low coolant or thermostat faults require separate cooling-system/range-performance diagnosis (P0116 or P0128 as applicable).
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 | failed coolant temperature sensor |
| 02 | open or shorted sensor wiring |
| 03 | connector corrosion |
| 04 | sensor ground fault |
| 05 | ECU input fault |
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