Fault codeP0115

MODERATE

Engine Coolant Temperature Circuit Malfunction

What this code means

Engine Coolant Temperature Circuit Malfunction.

P0115 is a generic code: it means the same thing on every make. P0115 belongs to family P01xx — Fuel and air metering. Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit has detected an electrical anomaly on this circuit without saying exactly which. Diagnosis starts with a visual check of the wiring and connector, then measuring the component — resistance, supply, ground — with a multimeter.

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.

What you notice

Hard starting, black smoke or high consumption when the control unit believes the engine is cold; a cooling fan running all the time, or a temperature gauge that does not match reality.

How to check it

Engine cold, Klaro's coolant temperature should be close to the outside temperature; it should then rise steadily as the engine warms. A reading that jumps or stays at −40 °C points to the wiring or connector. Also check the coolant level: a sensor sitting in air instead of liquid reads wrong.

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 →

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
15P0115