Manifold Absolute Pressure/Barometric Pressure Circuit

Possible causes

• CommonCracked, split or disconnected vacuum hose to the sensor
• CommonCarbon blocking the manifold port the sensor reads through
• CommonFailed sensor
• CommonCorroded or wet sensor connector
• PossibleVacuum leak elsewhere on the manifold, making the reading genuinely wrong
• PossibleWiring fault between sensor and module

What you might notice

• Rough running, hesitation or surging
• Poor fuel economy
• Black smoke, or a smell of unburnt fuel
• Hard starting
• Check engine light on

What to check, in order

1. Check the vacuum hose to the sensor before touching the sensor. A cracked or perished hose produces every one of these codes and costs almost nothing to replace - and on a sensor mounted directly to the manifold, check the port instead, because carbon blocks it.
2. Compare the sensor's reading at key-on, engine off, against the barometric reading. With the engine stopped the manifold is at atmospheric pressure, so the two should agree - this is the quickest test there is and it needs no tools beyond the scan tool.
3. Watch the live reading while the engine idles and then snaps to open throttle. It should drop to a strong vacuum at idle and rise sharply when the throttle opens.
4. Look for vacuum leaks before condemning the sensor. A large leak makes a healthy sensor report a pressure that is genuinely wrong, and the module blames the sensor.