What P0115 means
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.
How the engine computer detects it
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 Today it has largely been replaced by P0117, P0118 and P0119; GM and Ford do not set it in the tables checked.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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Poor cold or hot starting
- Radiator fan runs constantly
- Higher consumption, rough idle
- Temperature gauge implausible or dead
Common causes
- Connector corroded or loose, terminal spread Most likely
- Broken or chafed signal or ground wire Possible
- Sensor faulty internally (short, open, coolant inside) Possible
- Control module input or 5 V supply faulty Less likely
How to diagnose P0115
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: engine coolant temperature sensor, engine coolant temperature sensor wiring.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 1
- Fuel and air metering
- 15
- Specific fault
Questions drivers ask
Can I drive with code P0115?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0115?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0115 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0115 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.