P0115Engine Coolant Temperature Sensor 1 Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- The engine coolant temperature sensor 1 is an NTC thermistor: the control module feeds 5 V through a resistor, and as the coolant warms the resistance and signal voltage fall. Its value drives cold-start enrichment, idle speed, ignition timing, the radiator fan and the release of closed-loop mixture control. Some Ford engines measure cylinder head temperature instead and calculate a coolant value from it. P0115 is the general circuit fault without telling low from high. Today it has largely been replaced by P0117, P0118 and P0119; GM and Ford do not set it in the tables checked. Older or individual systems still use it as a collective code, for example Saab Trionic T5 (1998). The circuit is monitored continuously; when it fails, the module uses a substitute value and many systems run the radiator fan permanently.
- What you may notice
- Check engine light on
- Poor cold or hot starting
- Radiator fan runs constantly
- Higher consumption, rough idle
- Temperature gauge implausible or dead
- Likely causes
- LikelyConnector corroded or loose, terminal spread
- PossibleBroken or chafed signal or ground wire
- PossibleSensor faulty internally (short, open, coolant inside)
- RareControl module input or 5 V supply faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.