P0129
Barometric Pressure Too Low
- Severity
- Low
- Driving
- Drivable — book it in
The barometric pressure reading is below what the module considers possible. Barometric pressure tells the module how dense the air is, which is how it compensates fuelling for altitude and weather. On most vehicles this reading comes from the manifold pressure sensor, measured with the engine stopped, so a manifold pressure fault and a barometric fault are usually the same fault.
Possible causes
- CommonFailed manifold or barometric pressure sensor
- CommonVacuum reaching the sensor when it should be reading atmospheric pressure - a hose routed or connected wrongly after other work
- PossibleWiring or connector fault at the sensor
- RareGenuinely very high altitude, beyond the range the module was calibrated for
What you might notice
- Reduced power
- Rich or lean running, especially noticeable at altitude
- Poor fuel economy
- Check engine light on
What to check, in order
- Read the barometric value at key-on with the engine off and compare it against the local weather report. At sea level expect roughly 100 kPa, falling with altitude; a reading well below what the weather says is the sensor, not the weather.
- Check for a manifold pressure code stored alongside. The two normally share one sensor, so fixing that fixes this.
- Check the vacuum hose routing if anything was recently worked on. A sensor that should read atmospheric pressure but has been plumbed into manifold vacuum reads low all the time.
- Note the altitude the vehicle actually lives at before condemning anything. This code is occasionally correct.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Fuel and air metering
P0100P0101P0102P0103P0104P0105P0106P0107P0108P0109P0110P0111P0112P0113P0114P0115P0116P0117P0118P0119P0120P0121P0122P0123P0124P0125P0126P0127P0128P0129P0130P0131P0132P0133P0134P0135P0136P0137P0138P0139P0140P0141P0142P0143P0144P0145P0146P0147P0148P0149P0150P0151P0152P0153P0154P0155P0156P0157P0158P0159P0160P0161P0162P0163P0164P0165P0166P0167P0168P0169P0170P0171P0172P0173P0174P0175P0176P0177P0178P0179P0180P0181P0182P0183P0184P0185P0186P0187P0188P0189P0190P0191P0192P0193P0194P0195P0196P0197P0198P0199