P0118 Code: Engine Coolant Temperature Circuit High Input
🟠 Moderate severity · drivable
Drivable, but the computer may think the engine is cold, causing a rich mixture and poor fuel economy.
What P0118 means
The engine coolant temperature (ECT) sensor is reading very cold (high voltage), usually because the circuit is open or the sensor is faulty. The computer may think the engine is always cold.
Symptoms
- Check engine light is on
- Poor fuel economy
- Hard starting
- Temperature gauge reading wrong
- Black smoke from exhaust
Common causes
- most common: Faulty engine coolant temperature sensor (open circuit)
- common: Loose or corroded sensor connector
- less common: Low coolant level
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the engine coolant temperature sensor | Yes | $30–100 |
| Check and top up coolant if low | Yes | $10–30 |
| Repair open ECT wiring | Mechanic | $50–150 |
Frequently asked questions
Can I drive with a P0118 code?
Yes, but the engine may run rich and use more fuel. Fix it soon.
What is the most common cause of P0118?
A faulty coolant temperature sensor with an open circuit, or a loose connector.
How much does it cost to fix a P0118?
Typically $30–$100 for a new coolant temperature sensor.
Related codes
P0117
P0117 Code: Engine Coolant Temperature Circuit Low Input
P0115P0115 Code: Engine Coolant Temperature Circuit Malfunction
P0128P0128 Code: Coolant Thermostat (Coolant Temperature Below Regulating Temperature)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.