P0115
Medium SeverityEngine Coolant Temperature Sensor Circuit
Cooling System
What Does P0115 Mean?
The ECT sensor circuit has a general malfunction. This sensor tells the ECM how warm the engine is for fuel, timing, and fan control.
Common Fix
Replace ECT sensor
Estimated Cost (DIY)
$10 - $25
Symptoms
- ⚠️Check engine light
- ⚠️Electric fans running constantly or not at all
- ⚠️Poor fuel economy
- ⚠️Hard cold starting
Common Causes
Faulty ECT sensorlikely
Corroded connectorpossible
Wiring damagepossible
Thermostat stuck (incorrect actual temp)possible
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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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.