P0129Barometric Pressure Too Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The engine control module needs the ambient air pressure for mixture, altitude correction and boost limits. It comes either from a dedicated barometric sensor or from the MAP sensor, read at key-on with the engine stopped and updated at wide-open throttle. P0129 means this value is lower than physically possible – even on the highest drivable passes air pressure stays around 50 kPa, and GM and Ford use 50 kPa as their lower plausibility limit. Usual causes are a MAP or baro sensor reading too low, a blocked sensor port or high resistance in the wiring. No manufacturer document naming exactly this code was found: GM and Ford file the same finding under P2227.
- What you may notice
- Check engine light on
- Rich mixture, higher consumption, rough idle
- Loss of power (altitude-corrected boost limits)
- Likely causes
- LikelyMAP or baro sensor reading too low (dirty, oiled, drifted)
- PossibleHigh resistance or corrosion in signal wire or connector
- PossibleSensor port or hose blocked
- RareControl module (baro sensor often built in) or software
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.