P0129 means Barometric Pressure Too Low. The barometric pressure reading is lower than the computer expects, even allowing for altitude. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0129 means
Most engine sensors receive a 5-volt reference and return a signal between roughly 0 and 5 volts. Codes ending in circuit high or circuit low usually point to an electrical fault: an open circuit, a short or an unplugged connector. Range/performance codes mean a signal is present but disagrees with what the computer expects from the other sensors, which more often points to a dirty sensor, an air leak or a mechanical problem.
P0129 symptoms
- Check engine light
- Rough running on some vehicles
Common causes of P0129
- Failed MAP or barometric sensor
- Reference voltage or wiring fault
- Restricted sensor port
How to diagnose P0129
- Compare the barometric reading with local pressure for your altitude
- Check the MAP sensor reading key-on engine-off
- Check sensor wiring
Can you drive with P0129?
Usually yes.
P0129 tips
If you drive at high altitude, compare the reading with local barometric pressure before suspecting the sensor. On many engines the barometric reading comes from the MAP sensor at key-on before the engine starts, so a MAP sensor that reads low will also set this code; check the MAP sensor and its vacuum port first.
Will P0129 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0129 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0069 | Manifold Absolute Pressure – Barometric Pressure Correlation |
| P0105 | Manifold Absolute Pressure/Barometric Pressure Circuit |
| P0106 | Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance |
Guides that help
When it is more than a sensor
Sensor codes are usually fixed with a sensor, a connector, wiring or a leak repair rather than major parts. If testing turns up internal engine trouble instead, see how to tell if an engine is blown and compare engines by code on our engines page.
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