P0117
Engine Coolant Temperature Sensor Low Input
The ECT signal voltage is below threshold, which the ECU interprets as an implausibly hot coolant temperature (typical NTC sensor characteristic — low resistance at high temperature).
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Cabin heater weak or excessively hot
- Possible long warm-up time or hard cold start
Common causes
Ordered by how often each turns out to be the cause.
- Signal wire shorted to groundCommon
- Sensor failed shorted internallyPossible
Parts involved
- Coolant Temperature Sensor
- Coolant Temperature Sensor Wiring
P0117 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.