P0117 Toyota Corolla
Engine Coolant Temperature Sensor Circuit Low · Powertrain Code · Medium · Repair: Easy
What is P0117?
The coolant temperature sensor is reading lower than expected — possible open circuit or faulty sensor.
When the Toyota Corolla triggers code P0117 (engine coolant temperature sensor circuit low), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Toyota Corolla.
This repair is rated easy, meaning basic tools, no lift needed.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Toyota Corolla.
Common Causes on Toyota Corolla
- ECT sensor shorted to ground — resistance too low, reporting overly high temperature
- Coolant leak has corroded ECT sensor connector
- Internal short in Denso ECT sensor
- Pinched or grounded ECT signal wire in harness
Symptoms
- Check Engine Light on
- Temperature gauge pegged at hot even when engine is cold
- Cooling fans running at full speed immediately on startup
- Engine may not enter closed-loop fuel control
Notes for Toyota Corolla
Before replacing the ECT sensor, verify the issue with a multimeter — resistance should be about 2.5kΩ at room temperature and decrease as it warms up.