P0118: Coolant temperature sensor circuit high input

What P0118 means

The coolant sensor is reporting a very cold signal (open circuit), so the computer may think the engine is always cold.

Common symptoms

• Hard starting
• Worse fuel economy
• Cooling fan always on or never on
• Black smoke or sooty exhaust

Common causes

• Faulty coolant temperature sensor
• Damaged wiring, corroded connector or blown fuse

Can I keep driving?

Fix soon. Usually drivable for a short time, but get it checked soon. Ignoring it can waste fuel, raise emissions and lead to more damage.

What to do next

1. Write down the code and any symptoms you notice.
2. Check the simple things first: the fuel cap, loose connectors and fluid levels where they apply.
3. Do not just clear the code. If the light comes back, the cause is still there and needs a proper diagnosis.
4. Read live data and freeze frame data with an OBD-II scanner app to see what the car was doing when the code was set.

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