P0118: Engine Coolant Temperature (ECT) Sensor 1 Circuit High
The coolant temperature sensor signal voltage is higher than a working sensor can produce. Usually an open wire, unplugged connector, or failed sensor.
Green, yellow, red: three ways P0118 can look
The same code can be a quick fix or a reason to pull over. Match your situation to the closest example.
Keep an eye on it
Code set once and the vehicle drives normally.
Schedule a repair
Code keeps returning or you notice drivability changes. Get the sensor and wiring tested.
Stop and get help
Temperature gauge reading wrong with signs of overheating like steam or a sweet smell. Shut it off and check coolant.
Symptoms you might notice
- Check engine light
- Possible rough running or poor economy
Common causes, cheapest first
- Unplugged or loose connector
- Failed coolant temperature sensor
- Broken signal or ground wire
What you can check before calling
- Check the coolant temperature sensor connector is fully seated and clean
- Look for damaged wiring near hot or moving parts
A code points to a system, not a part. Replacing parts based on the code alone is how people spend money without fixing the problem. Testing confirms the cause first.
Generic codes (second character 0) mean the same thing on every vehicle. Some manufacturers add their own details, so check service information for your exact vehicle.
Related codes
More cooling & temperature codes
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does P0118 mean?
P0118 means "Engine Coolant Temperature (ECT) Sensor 1 Circuit High". The coolant temperature sensor signal voltage is higher than a working sensor can produce. Usually an open wire, unplugged connector, or failed sensor.
Can I drive with code P0118?
It depends on what the vehicle is doing. Green: Code set once and the vehicle drives normally. Yellow: Code keeps returning or you notice drivability changes. Get the sensor and wiring tested. Red: Temperature gauge reading wrong with signs of overheating like steam or a sweet smell. Shut it off and check coolant.
What causes P0118?
The most common causes are: unplugged or loose connector; failed coolant temperature sensor; broken signal or ground wire.
Is P0118 a serious code?
It can be. Temperature gauge reading wrong with signs of overheating like steam or a sweet smell. Shut it off and check coolant.
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