Engine Coolant Temperature (ECT) Circuit Malfunction
What does this mean?
The ECT sensor measures coolant temperature to help the PCM adjust fuel injection and ignition timing. Code P0115 indicates a general circuit malfunction.
Disclaimer: This diagnostic code is part of the standard OBD2 system and can apply to Toyota C-hr models manufactured from 1996 to 2026. However, please note that the presence of this specific code depends on your vehicle's exact engine configuration, options, and production year.
Common Causes
Faulty Engine Coolant Temperature (ECT) sensor
Damaged, chafed, or broken wiring harness
Corroded or loose electrical connector
Faulty or stuck thermostat
Symptoms to Watch For
- Check Engine Light is illuminated
- Difficulty starting the engine
- Decreased fuel economy
- Rough or unstable idle
- Engine stalls when cold
- Cooling fan not operating
How to Diagnose
Common Solutions
**Replace the Engine Coolant Temperature (ECT) Sensor:** This is the most common solution. If the sensor fails the resistance tests, provides erratic readings, or is physically damaged, replacing it with a high-quality OEM or equivalent aftermarket sensor will typically resolve the P0115 code.
**Repair or Replace Damaged Wiring and/or Connectors:** If the diagnostic steps reveal an open circuit, short circuit, or a corroded/damaged electrical connector, the affected wiring harness section or connector pigtail must be professionally repaired or replaced. Ensure all repairs involve proper soldering, heat-shrink tubing, and secure connections to prevent future issues.
**Address Poor Ground Connections:** A poor or corroded ground connection for the ECT sensor circuit can cause a circuit malfunction. Ensure all ground points are clean, tight, and free of corrosion, providing a solid electrical path back to the PCM.
**PCM Replacement (Rare):** Only consider replacing the Powertrain Control Module (PCM) as a last resort, after thoroughly ruling out the ECT sensor, all associated wiring, and connectors. A faulty PCM could be unable to provide the necessary 5V reference, process the sensor's signal correctly, or provide a proper ground. This is a costly repair and often requires reprogramming.