P0129 code meaning
Barometric Pressure Too Low
Powertrain system Generic code P01xx codes Check engine light
What P0129 means
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.
P0129 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0129
- Check engine light on
- Rich mixture, higher consumption, rough idle
- Loss of power (altitude-corrected boost limits)
Common causes of P0129
- Most likelyMAP or baro sensor reading too low (dirty, oiled, drifted)
- PossibleHigh resistance or corrosion in signal wire or connector
- PossibleSensor port or hose blocked
- Less likelyControl module (baro sensor often built in) or software
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Barometric pressure sensorManifold absolute pressure sensorSensor wiring
What each part of P0129 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 1 | Area: fuel and air metering. |
| 29 | The exact fault in that area. |
What to do next
- Note P0129 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0129
What does P0129 mean?
P0129 means "Barometric Pressure Too Low". The engine control module needs the ambient air pressure for mixture, altitude correction and boost limits. It is a generic code, so it means the same on every make.
Is it safe to drive with P0129?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0129 fail an emissions test?
Yes, it can. P0129 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0129 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0129 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.