P0118 on a Subaru: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Safe to drive, but the engine may run rich and use more fuel until the sensor circuit is repaired.

What P0118 means on a Subaru

On a Subaru, P0118 means the engine coolant temperature (ECT) sensor is sending a high-voltage signal that the computer reads as the engine being very cold. On many Subaru engines the sensor sits on top of the engine near the throttle body, and an open circuit from a failed sensor or broken wire is the usual cause. The computer then enriches the fuel mixture as if the engine were cold.

Is P0118 common on Subarus?

P0118 is common on higher-mileage Outback and Forester models. Subaru engine compartments are hard on connectors, so corrosion and wires that break at the sensor are frequent findings. A slow coolant leak from a hose or the radiator can also affect the sensor area.

Commonly reported on: Outback, Forester, Impreza, Crosstrek.

Symptoms

Check engine light on
Poor fuel economy
Hard cold start
Engine runs rich

Common causes

most common: Faulty coolant temperature sensor
common: Open sensor signal wire
common: Corroded or loose connector
less common: Coolant leak affecting the sensor area

How to fix it

Fix	DIY?	Typical cost
Replace the coolant temperature sensor	Yes	$25–70
Repair the sensor wiring or connector	Mechanic	$50–150
Have a shop diagnose the circuit	Mechanic	$80–120

Frequently asked questions

Can I drive my Subaru with a P0118 code?

Yes. The engine will run rich and use more fuel, but it is not an emergency. Fix the circuit soon to restore fuel economy.

Why does P0118 happen on Subarus?

A failed coolant temperature sensor is the most common cause, with corroded connectors and broken wires common on higher-mileage Outbacks and Foresters.

How much does it cost to fix P0118 on a Subaru?

A replacement sensor is about $25 to $70, plus labor if a shop does it. Wiring repairs run about $50 to $150.