Engine Coolant Temperature Sensor Low Input
Diagnose P0117 coolant temperature sensor code. Learn why the ECT reads low and how to test and replace it.
What you may notice
Symptoms
- 01Check engine light on
- 02Cooling fans running constantly
- 03Rich running condition
- 04Poor fuel economy
- 05Possible black smoke from exhaust
Where to look first
Common causes
- 01Short to ground in the ECT circuit
- 02Failed coolant temperature sensor
- 03Damaged wiring or connector
- 04Corroded connector pins
- 05ECM fault (rare)
Step by step
What to check and repair
- 01Inspect ECT wiring for shorts to ground
- 02Check the connector for corrosion
- 03Test the sensor resistance against spec
- 04Repair damaged wiring
- 05Replace the coolant temperature sensor if faulty
What Does P0117 Mean?
The P0117 code indicates that the Engine Coolant Temperature (ECT) sensor is sending a signal indicating an extremely high temperature (low voltage), often beyond what's realistically possible.
What This Usually Means
Rather than the engine actually being that hot, P0117 typically points to a short to ground in the sensor or wiring, or a failed sensor reading incorrectly.
Why ECT Data Matters
The ECM uses coolant temperature to control fuel mixture, fan operation, and ignition timing. A bad reading can cause a rich condition, poor starts, and cooling fan issues.
How AI4Car Helps
AI4Car can display the live coolant temperature reading, letting you compare it to the actual engine temperature to confirm whether the sensor is reading correctly.