Symptoms of P0115
- Check-engine light on, sometimes with rough or uneven running.
- Hesitation, surging, or a noticeable change in fuel economy.
- Occasionally hard starting or a smell of unburnt fuel.
Common causes of P0115
- A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
- Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
- Wiring, connector, or fuel-delivery problems that skew the reading.
Useful checks before replacing parts
- Compare coolant temperature with ambient, intake temperature, and actual engine temperature after cold soak and during warm-up.
- Check sensor signal voltage, reference, ground, connector condition, harness routing, coolant intrusion, and thermostat-related symptoms.
- Review fan operation, cold-start fueling, gauge data, and companion thermostat or overtemperature codes.
Related OBD-II codes
These nearby fuel / air entries can help compare wording and pin down the fault area.