P0115moderate severityPowertrain
Engine Coolant Temperature (ECT) Sensor 1 Circuit
on 2020 Mazda Mazda3 2.0L I4 · AWD
What this code means
General malfunction in the engine coolant temperature sensor circuit.
Symptoms
- Check Engine Light
- Poor fuel economy
- Hard starting
- Incorrect temp gauge reading
- Fans not operating correctly
Common causes
- Faulty ECT sensor
- Wiring damage
- Corroded connector
- Low coolant level
Diagnostic steps
- Test ECT resistance at known temperature
- Inspect wiring
- Check coolant level
- Compare ECT to IAT at cold start
Repair notes
Replace ECT sensor or repair wiring. Verify coolant level.
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