OBD CodesWhat it means
The coolant temperature sensor tells the computer how hot the engine is. The computer uses it for cold-start fuelling, idle speed, the radiator fan and, on many cars, the temperature gauge. With a bad signal the engine may run too rich, or the fan may run all the time.
Codes in this group
| Code | Meaning |
|---|---|
| P0115 | Coolant temperature sensor circuit fault |
| P0116 | Coolant temperature reading out of the expected range |
| P0117 | Coolant temperature signal too low (reads very hot) |
| P0118 | Coolant temperature signal too high (reads very cold) |
| P0119 | Coolant temperature signal cuts in and out |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Hard starting, hot or cold
- Radiator fan running constantly, or not at all
- Temperature gauge reading wrongly
- Black smoke and high fuel use
Common causes
Most likely first:
- Low coolant level, leaving the sensor dry
- A corroded plug or broken wire
- A failed sensor
- A thermostat stuck open (with P0116)
What to check first
- With the engine cold, check the coolant level in the expansion tank
- Look for coolant leaks
- Check the sensor plug for green or white corrosion
- Never open the radiator cap on a hot engine
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
Mass air flow (MAF) sensor (P0100), Manifold pressure (MAP) and barometric sensor (P0105), Intake air temperature sensor (P0110), Thermostat and engine warm-up (P0125), Throttle position sensor (P0120), Accelerator pedal sensor and throttle agreement (P2120), Electronic throttle actuator (P2100), Oxygen sensor before the catalytic converter (sensor 1) (P0130). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.