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

P0115

P0115 Code: Engine Coolant Temperature Circuit Malfunction

P0128

P0128 Code: Coolant Thermostat (Coolant Temperature Below Regulating Temperature)

P0118 by vehicle brand

Causes and repair costs for P0118 differ between makes. Pick your brand for the specifics.

P0118 on a Mercedes-Benz

Volkswagen

P0118 on a Volkswagen

Updated 2026-08. This page is informational and not a substitute for professional diagnosis.