Engine Coolant Temperature Sensor 1 Circuit
What does P0115 mean?
The P0115 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Sensor 1 Circuit. This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Temperature gauge erratic or pegged
- Poor fuel economy
- Rich running
- Hard cold starts
Probable Causes (Ranked by Likelihood)
- Faulty ECT sensor Very High
- Wiring harness damage at sensor connector High
- Corrosion at ECT sensor connector High
- Open or short in ECT circuit wiring Moderate
- PCM input circuit fault Low
Step-by-Step Diagnostic Procedure
-
With key on/engine cold, ECT sensor should read near ambient temperature. A reading of -40F or above 300F indicates a circuit fault.
-
Inspect the sensor connector for corrosion, bent pins, or green residue from coolant leaks.
-
Measure ECT sensor resistance cold (typically 2,000-3,000 ohms at 70F) and compare to spec chart.
-
Check wiring from sensor to PCM for opens or shorts.
-
Replace sensor and retest.
Frequently Asked Questions
Can a bad ECT sensor cause overheating?
Not directly, but a faulty reading may prevent the radiator fan from engaging on time. Additionally, if the gauge reading is inaccurate, you may not notice genuine overheating until it is too late. Address ECT codes promptly.