P0109: Manifold Absolute Pressure/Barometric Pressure Sensor Circuit Intermittent
P0109 means Manifold Absolute Pressure/Barometric Pressure Sensor Circuit Intermittent. The manifold absolute pressure (MAP) sensor measures intake manifold pressure (vacuum), which the engine computer uses to calculate engine load. The signal drops out or jumps erratically. Intermittent faults are most often caused by loose or corroded connectors and chafed wiring rather than the sensor itself.
Can I keep driving? Drivable with care. Diagnose soon: performance, economy or other components can be affected.
Common symptoms
- Check engine light on
- Rough idle or hesitation
- Poor fuel economy or black smoke
- Hard starting
- Possible failed emissions
Possible causes
- Cracked or disconnected vacuum hose to the sensor
- Failed MAP sensor
- Wiring or connector fault
- Problem with the 5 V reference circuit
- Engine mechanical problem causing low vacuum (range/performance codes)
How to diagnose P0109
- Check the vacuum hose or port to the sensor.
- With key on, engine off, the MAP reading should match barometric pressure. At warm idle it should drop considerably.
- Check the 5 V reference, ground and signal at the connector.
- For range/performance codes, verify engine vacuum with a gauge.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Related codes
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.