Fault codeP0118

MODERATE

Engine Coolant Temperature Circuit High Input

What this code means

Engine Coolant Temperature Circuit High Input.

P0118 is a generic code: it means the same thing on every make. P0118 belongs to family P01xx — Fuel and air metering. Its page explains how to read a code and groups all its codes by part.

Coolant temperature sensor

This sensor, screwed into the cooling circuit near the cylinder head, tells the control unit how warm the engine is. It is one of the most important inputs: it sets the cold-start enrichment, the idle speed, the cooling fan and the moment the mixture regulation switches to closed loop.

Symptoms

Hard starting, high consumption, black smoke when cold, cooling fan running permanently, temperature gauge reading nothing or pegged. The coolant temperature sensor is returning a value out of range — the control unit no longer knows whether the engine is cold or hot, and injects by guesswork.

Common causes

Faulty coolant temperature sensor — a common, cheap part
Corroded connector, often from coolant that has seeped
Wire cut, shorted, or failed ground
Coolant level very low, leaving the sensor in air

How to diagnose it

Compare the temperature shown in live data with reality: engine cold in the morning, it should match the ambient temperature, then climb to 85 to 95 °C while driving. A value frozen at −40 °C or 140 °C points to the electrical circuit.

Check the connector and measure the sensor's resistance cold then warm; compare with the manufacturer's figures. Check the coolant level while you are there.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Coolant temperature
Intake air temperature
Time since engine start

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

Repair cost

Sensor: €10 to €40, fitting €20 to €60 — some coolant sometimes has to be drained. Connector repair: €20 to €80.

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
18P0118