P0115
Engine Coolant Temperature Sensor 1 Circuit
Fuel & air metering
Generic OBD-II
High
What it means
P0115 means the computer sees a problem in the engine coolant temperature (ECT) sensor circuit. That reading is used to set cold-start fueling and control the cooling fans, so a fault can cause hard cold starts, rich running, poor economy, and mismanaged fans — occasionally leading to overheating if it's ignored.
High
Can I keep driving? Usually drivable, but a bad coolant-temp signal can cause hard cold starts, rough running, and poor economy, and it can interfere with fan and overheating protection — fix it soon.
Common symptoms
What you'll notice
- Check-engine light on
- Hard starting when cold, or rough running until warmed up
- Poor fuel economy (engine may run rich)
- Cooling fans running constantly or not engaging
Common causes
Most likely first
- Faulty engine coolant temperature (ECT) sensorLikely
- Corroded, loose, or damaged connector at the sensorCommon
- Open or shorted wiring in the ECT sensor circuitCommon
- Low coolant level leaving the sensor uncoveredLess often
- Rarely, an ECM/PCM faultLess often
How to diagnose & fix
Work through it in order
- Read live data and compare the coolant-temp reading with the intake-air temp on a cold engine — they should be close at cold start.
- Inspect the ECT sensor connector for corrosion and a secure fit.
- Check the signal and ground wires for opens and shorts back to the ECM.
- Measure the sensor's resistance against spec across temperatures; replace it if out of range.
- Confirm coolant level and condition. Clear the code and re-test through a full warm-up.
FAQ
Quick answers
Is it safe to drive with P0115?+
Short-term, usually yes, but the engine may start hard when cold and run rich, and the computer may mismanage the cooling fans. Because that can lead to overheating, don't leave it unaddressed.
Can I just clear P0115?+
It will return until the sensor or wiring is repaired. The ECT signal is used constantly for fueling and fan control, so the fault reappears quickly.
Related codes
Often seen with P0115
Read & clear P0115 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX