P0115 Code: Engine Coolant Temperature Circuit Malfunction
🟠 Moderate severity · drivable
Drivable, but the computer gets a wrong coolant-temperature reading, which can cause poor running and fuel economy.
What P0115 means
The engine coolant temperature (ECT) sensor circuit is malfunctioning, so the computer can't tell the engine's temperature. The ECT reading controls the fuel mixture, especially during warm-up.
Symptoms
- Check engine light is on
- Poor fuel economy
- Hard starting when cold
- Temperature gauge reading wrong
- Possible rough running
Common causes
- most common: Faulty engine coolant temperature sensor
- common: Damaged wiring or loose connector
- less common: Low coolant level
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Inspect and clean the ECT sensor connector | Yes | $0–10 |
| Replace the engine coolant temperature sensor | Yes | $30–100 |
| Check and top up coolant if low | Yes | $10–30 |
Frequently asked questions
Can I drive with a P0115 code?
Yes, but the engine may run poorly and use more fuel. Fix it soon.
What is the most common cause of P0115?
A faulty engine coolant temperature sensor. It's an inexpensive, easy-to-replace part.
How much does it cost to fix a P0115?
Typically $30–$100 for a new coolant temperature sensor.
Related codes
P0117
P0117 Code: Engine Coolant Temperature Circuit Low Input
P0118P0118 Code: Engine Coolant Temperature Circuit High Input
P0128P0128 Code: Coolant Thermostat (Coolant Temperature Below Regulating Temperature)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.