What does P0118 mean?
The engine coolant temperature (ECT) sensor tells the computer how hot the engine is. It affects fuel mixture, idle speed, cooling fans and, on many cars, the temperature gauge.
High voltage on a temperature sensor means the computer sees an open circuit and reads extremely cold.
Codes are a starting point. They tell you which test failed, not which part to replace. Check for other stored codes and fix those in a sensible order.
Symptoms
- Check engine light
- Hard starting
- Cooling fans running all the time (a common fail-safe)
- Poor fuel economy
- Wrong temperature gauge reading on some vehicles
Common causes
- Sensor unplugged or connector broken
- Open signal or ground wire
- Sensor open internally
How to diagnose P0118
- Look at live data: an open circuit will read around -40 F.
- Jumper the two connector pins together with a fused jumper. The reading should swing to a very hot value. If it does, the sensor is open; if not, check the wiring.
- Check sensor resistance against the service spec.
- Check the coolant level first (only when the engine is cold).
- Compare ECT with intake air temperature after an overnight cold soak.
How to fix it
- Top up or bleed the cooling system
- Repair wiring
- Replace the ECT sensor
Estimated repair cost
Likely repairs for P0118 run from about $80 to $250, depending on the cause.
| Repair | Typical range (parts + labor) |
|---|---|
| Diagnostic fee (scan + testing) | $100 - $200 |
| Coolant temperature sensor | $80 - $250 |
These are rough US estimates for an independent shop in 2026, based on typical parts prices and standard labor times. Dealers, big trucks, luxury brands and high-cost areas often run higher. They are not quotes. Use the repair cost estimator to adjust for your vehicle.
How serious is P0118?
Moderate severity
Usually drivable, but keep an eye on the real engine temperature. If it is overheating, stop.
P0118 FAQ
What does P0118 mean?
P0118 stands for "Engine Coolant Temperature Sensor 1 Circuit High". The engine coolant temperature (ECT) sensor tells the computer how hot the engine is.
Can I drive with a P0118 code?
Usually drivable, but keep an eye on the real engine temperature. If it is overheating, stop.
How much does it cost to fix P0118?
It depends on the cause. The likely repairs for P0118 range from about $80 to $250 at an independent shop in the US, plus a diagnostic fee of roughly $100-$200. These are rough estimates; dealer prices and some vehicles run higher.
What is the most common cause of P0118?
The most common causes are: sensor unplugged or connector broken; open signal or ground wire; sensor open internally.