P0115 Engine coolant temperature sensor 1 circuit
What P0115 means
The engine computer has a problem with the signal from the engine coolant temperature (ECT) sensor. It uses this reading to set fuelling, idle speed and the cooling fans, so it falls back to a default value and often runs the fans constantly as a precaution.
P0115 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 40–180 €
- Workshop time
- 0.3–1.5 h
- Repair difficulty
- Easy
- DIY possible
- Yes
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Temperature gauge reads wrong or stays at minimum
- Hard cold starts or long warm-up
- Higher fuel consumption
Common causes
- Failed coolant temperature sensor
- Corroded or loose sensor connector
- Damaged wiring between the sensor and the engine computer
- Low coolant level leaving the sensor in air
Can I keep driving with P0115?
You can drive, but have it checked within a week. Watch the coolant level, because the temperature gauge may use the same faulty sensor and might not warn you of overheating.
What to check first
- Check the coolant level with the engine cold and top up if low.
- Read the live coolant temperature: on a cold engine it should match the outside temperature and rise smoothly when the engine runs.
- Inspect the sensor connector for corrosion and check the wiring for damage.
- Measure the sensor resistance against the specification and replace the sensor if it is out of range.
Related codes
- P0116 Engine coolant temperature sensor 1 range/performance
- P0113 Intake air temperature sensor 1 circuit high (bank 1)
- P0117 Engine coolant temperature sensor 1 circuit low
- P0112 Intake air temperature sensor 1 circuit low (bank 1)
- P0118 Engine coolant temperature sensor 1 circuit high
- P0111 Intake air temperature sensor 1 range/performance (bank 1)
- P0110 Intake air temperature sensor 1 circuit (bank 1)
- P0120 Throttle/pedal position sensor A circuit
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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