P0117
Medium SeverityEngine Coolant Temperature Sensor Circuit Low
Cooling System
P0117 — Instant Answer
Engine Coolant Temperature Sensor Circuit Low
Severity: MEDIUM SEVERITY
Meaning: ECT sensor voltage is too low, indicating an impossibly high temperature. Usually a shorted sensor.
Safe to drive? Usually yes with caution, but confirm root cause before long trips.
Estimated repair cost: $10 - $25
Most common causes:
- 1. Shorted ECT sensor (35-45% of cases)
- 2. Short in sensor wiring (10-25% of cases)
- 3. Corroded connector pins (10-25% of cases)
Symptoms
- ⚠️Fans running at max speed constantly
- ⚠️Rich fuel mixture
- ⚠️Check engine light
- ⚠️Temp gauge pegged high
Related Symptoms
Common Causes
How to Diagnose P0117
- 1Disconnect sensor — fans should stop, gauge should change
- 2Measure sensor resistance
- 3Check wiring for shorts to ground
- 4Replace sensor
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Repair guides, symptom pages, and wiring diagrams related to P0117.
Related Codes
The ECT sensor circuit has a general malfunction. This sensor tells the ECM how warm the engine is for fuel, timing, and fan control.
ECT sensor voltage is above maximum, reading as extremely cold. Usually an open sensor circuit.
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.
Frequently Asked Questions
- Why are my fans always on with P0117?
- The shorted sensor tells the ECM the engine is overheating, so it runs the fans at max. The engine is likely at normal temperature.
- Can P0117 cause overheating?
- No — it makes the ECM think the engine is hot, but actual temperature is fine. However, always verify with an IR thermometer.
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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