Fault codeP0109

MODERATE

Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

What this code means

Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent.

P0109 is a generic code: it means the same thing on every make. P0109 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 signal drops out or jumps from time to time. This is typical of a poor contact: a loose or corroded connector, or a chafed wire that touches intermittently, often triggered by vibration or heat. The fault may disappear and come back; checking the wiring with the engine running is often revealing.

Manifold pressure sensor (MAP)

The MAP sensor measures the pressure, or vacuum, inside the intake manifold. On many engines it is the main measure of engine load; on others it supplements the airflow sensor. It is often combined with the barometric pressure reading used to correct for altitude.

What you notice

Hesitation, poor acceleration, rough idle, higher consumption, and black smoke on diesels.

How to check it

Check the sensor's vacuum hose if it has one (split, disconnected or full of oil), its connector, and the intake for leaks. Engine off, the manifold pressure and the barometric pressure should be almost the same; at idle on a petrol engine the manifold pressure should drop to roughly 30 kPa. Klaro shows both.

Watch it live in Klaro

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

Intake manifold pressure
Barometric pressure
Mass air flow

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
09P0109