P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

P0109 indicates an intermittent manifold absolute pressure or barometric pressure circuit fault. The pressure signal drops out or becomes unstable.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not clear intermittent MAP/BARO faults without stressing the connector, harness, and vacuum source.

Symptoms of P0109

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0109

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Graph MAP and BARO data during vibration, throttle changes, boost or vacuum transitions, and harness movement.
Inspect connector tension, sensor port contamination, wiring rub points, shared reference circuits, and moisture intrusion at the sensor.
Compare signal dropouts with engine load, RPM, misfire, hesitation, or related airflow and fuel trim codes.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.