P0115
Medium SeverityEngine Coolant Temperature Sensor Circuit
Cooling System
P0115 — Instant Answer
Engine Coolant Temperature Sensor Circuit
Severity: MEDIUM SEVERITY
Meaning: The ECT sensor circuit has a general malfunction. This sensor tells the ECM how warm the engine is for fuel, timing, and fan control.
Safe to drive? Usually yes with caution, but confirm root cause before long trips.
Estimated repair cost: $10 - $25
Most common causes:
- 1. Faulty ECT sensor (35-45% of cases)
- 2. Corroded connector (10-25% of cases)
- 3. Wiring damage (10-25% of cases)
- 4. Thermostat stuck (incorrect actual temp) (10-25% of cases)
Symptoms
- ⚠️Check engine light
- ⚠️Electric fans running constantly or not at all
- ⚠️Poor fuel economy
- ⚠️Hard cold starting
Related Symptoms
Common Causes
How to Diagnose P0115
- 1Check ECT sensor connector
- 2Measure sensor resistance vs actual temp
- 3Inspect wiring for damage
- 4Compare ECT reading to IAT reading on cold start (should be similar)
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Related Resources
Repair guides, symptom pages, and wiring diagrams related to P0115.
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Related Codes
The ECT sensor reading is not changing as expected during warm-up. Either the sensor is lazy or the thermostat is preventing normal warm-up.
ECT sensor voltage is too low, indicating an impossibly high temperature. Usually a shorted sensor.
ECT sensor voltage is above maximum, reading as extremely cold. Usually an open sensor circuit.
Frequently Asked Questions
- What happens if the coolant temp sensor fails?
- The ECM cannot properly manage fuel mixture, fan operation, and idle speed. You may get poor fuel economy and the engine may run rough.
- Are ECT sensors easy to replace?
- Usually yes — they screw into the engine block or intake manifold. Drain some coolant first.
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Author & Review
Written by AllOEMManuals Editorial Team. Reviewed by ASE-certified technicians and updated with factory-reference checks for fitment-sensitive steps.
This guide was drafted with AI assistance and reviewed for accuracy by a human editor.
Last updated: 2026-05-07