Fuel & air metering · Powertrain · generic (SAE-defined)
P0115: Engine Coolant Temperature Circuit
P0115 means the engine computer detected a general electrical problem in the engine coolant temperature (ECT) sensor circuit, so it cannot reliably read engine temperature.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0115 sets
The engine coolant temperature (ECT) sensor is a thermistor that changes resistance with temperature. The powertrain control module (PCM) supplies a reference voltage and reads the signal. If the signal is missing, erratic or outside the circuit's normal range in a way not covered by a specific high or low code, P0115 sets. Many PCMs then run the cooling fans continuously as a precaution.
Common causes of P0115
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Faulty ECT sensor
- Loose, corroded or damaged connector
- Open or shorted sensor wiring
- Coolant leaking into the connector
- PCM fault (rare)
P0115 symptoms
- Check engine light on
- Cooling fans running constantly
- Hard starting, especially when cold
- Poor fuel economy or black smoke
- Erratic or missing temperature gauge reading
How P0115 is diagnosed
- Scan for codes and compare ECT reading to actual engine temperature
- Inspect the sensor connector and harness
- Measure reference voltage and ground at the connector
- Measure sensor resistance at a known temperature
- Wiggle-test wiring while watching live data
- Replace the sensor or repair wiring, then confirm stable readings
Typical fixes for P0115
- Replace the ECT sensor
- Repair wiring or replace the connector
- Fix coolant leaks around the sensor
- Bleed air from the cooling system after sensor replacement
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0115 FAQ
What does code P0115 mean?
P0115 means the engine computer detected a general electrical problem in the engine coolant temperature (ECT) sensor circuit, so it cannot reliably read engine temperature. The standard definition is "Engine Coolant Temperature Circuit."
Can I drive with a P0115 code?
You can usually drive a short distance, but watch the temperature gauge closely, as it may be inaccurate. If there are any signs of overheating such as steam or a high gauge reading, stop and turn the engine off.
Why are my radiator fans always on with P0115?
When the PCM cannot trust the coolant temperature reading, many systems run the fans continuously to prevent overheating.
Is the dashboard temperature gauge accurate with P0115?
Not necessarily. On many vehicles the gauge uses the same sensor, so it may read wrong. Check coolant level and watch for steam or overheating signs.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.