A faulty barometric pressure sensor, or MAP sensor where the two are combined (both sources; RepairPal lists MAP sensor replacement as a common repair). Corroded connector at the sensor (OBD-Codes.com). Open or shorted wiring, or a poor ground, at the MAP or barometric pressure sensor (both sources). Low engine vacuum from engine wear, an ignition misfire or a clogged catalytic converter (OBD-Codes.com); RepairPal lists internal engine failure, incorrect engine timing and a vacuum leak. Mass air flow (MAF) sensor failure (RepairPal); OBD-Codes.com notes combined MAF/BPS sensors can be thrown off by a very dirty air filter. A failed PCM or PCM programming error (OBD-Codes.com, as a last possibility).

Repair a corroded connector, damaged wiring or poor sensor ground (OBD-Codes.com notes some designs need an added ground, depending on the maker). Fix a vacuum leak or the engine problem causing low vacuum, such as misfires, a clogged catalytic converter or incorrect timing. Replace the barometric pressure or MAP sensor if it fails testing. Replace a failed MAF sensor where it's the cause (RepairPal). Correct timing problems, including timing belt replacement where needed (RepairPal lists timing belt replacement as a common repair). Reprogram or replace the PCM only after everything else checks out.

P0129🔧 Barometric pressure (BARO) / MAP sensor inputDrive with caution, fix soon

P0129: Barometric Pressure Too Low (Meaning, Causes, Fixes)

Q: What does P0129 mean?

P0129 means the engine computer (PCM) is reading barometric (outside air) pressure lower than it expects, from either a separate barometric pressure sensor or the MAP sensor. Common causes include a corroded sensor connector, a bad sensor or wiring, and low engine vacuum from engine wear, misfires or a clogged catalytic converter. Barometric pressure changes with altitude and weather, and the PCM uses it to help calculate fuel delivery and ignition timing. OBD-Codes.com explains that P0129 sets when the PCM detects a low barometric pressure reading from the barometric pressure sensor (BPS) or the manifold absolute pressure (MAP) sensor that differs from its comparison data by more than a programmed limit. Designs vary: most makers use a separate BPS mounted away from the engine, often with a vacuum hose, while some build it into the MAP sensor (or, on some systems, the MAF sensor housing). RepairPal describes the code as the PCM's intake pressure sensor signal being too low. The code is generic to OBD-II vehicles (1996 and newer); OBD-Codes.com names Dodge, Chrysler, Hyundai, Jeep and Mazda as examples, and search interest shows people look it up most for Dodge (including the Ram 1500), Jeep and Chrysler, so check technical service bulletins (TSBs) for your vehicle.

Q: Can I keep driving with P0129?

Drive with caution, fix soon. Usually drivable for a short time, but get it diagnosed soon. RepairPal rates P0129 'Moderate', meaning it may not threaten safety right away but should be checked within a reasonable time. OBD-Codes.com lists a rich-running condition, hesitation and black smoke among the symptoms, and a rich engine can foul plugs and stress the catalytic converter over time. If the engine is misfiring, hesitating badly or blowing black smoke, keep driving to a minimum until it's fixed.

Reviewed 2026-10-26 · Based on 2 cited source(s)

What P0129 means

Barometric pressure changes with altitude and weather, and the PCM uses it to help calculate fuel delivery and ignition timing. OBD-Codes.com explains that P0129 sets when the PCM detects a low barometric pressure reading from the barometric pressure sensor (BPS) or the manifold absolute pressure (MAP) sensor that differs from its comparison data by more than a programmed limit. Designs vary: most makers use a separate BPS mounted away from the engine, often with a vacuum hose, while some build it into the MAP sensor (or, on some systems, the MAF sensor housing). RepairPal describes the code as the PCM's intake pressure sensor signal being too low. The code is generic to OBD-II vehicles (1996 and newer); OBD-Codes.com names Dodge, Chrysler, Hyundai, Jeep and Mazda as examples, and search interest shows people look it up most for Dodge (including the Ram 1500), Jeep and Chrysler, so check technical service bulletins (TSBs) for your vehicle.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable for a short time, but get it diagnosed soon. RepairPal rates P0129 'Moderate', meaning it may not threaten safety right away but should be checked within a reasonable time. OBD-Codes.com lists a rich-running condition, hesitation and black smoke among the symptoms, and a rich engine can foul plugs and stress the catalytic converter over time. If the engine is misfiring, hesitating badly or blowing black smoke, keep driving to a minimum until it's fixed.

Common symptoms

Check engine light on (OBD-Codes.com says the light may come on)
Lack of engine performance or decreased performance (both sources)
Lower fuel economy (both sources)
Rich running, hesitation on acceleration and black smoke from the exhaust (OBD-Codes.com)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

A faulty barometric pressure sensor, or MAP sensor where the two are combined (both sources; RepairPal lists MAP sensor replacement as a common repair)
Corroded connector at the sensor (OBD-Codes.com)
Open or shorted wiring, or a poor ground, at the MAP or barometric pressure sensor (both sources)
Low engine vacuum from engine wear, an ignition misfire or a clogged catalytic converter (OBD-Codes.com); RepairPal lists internal engine failure, incorrect engine timing and a vacuum leak
Mass air flow (MAF) sensor failure (RepairPal); OBD-Codes.com notes combined MAF/BPS sensors can be thrown off by a very dirty air filter
A failed PCM or PCM programming error (OBD-Codes.com, as a last possibility)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes and freeze frame data and write them down. OBD-Codes.com says to fix misfire, fuel system and catalytic converter codes before chasing P0129.
Inspect the wiring and connector at the MAP or barometric pressure sensor (and MAF sensor if the baro sensor is built into it) for damage or corrosion.
Check the sensor's vacuum hose, if it has one, and look and listen for vacuum leaks.
Check the air filter and replace it if it's very dirty.
Clear the code and test-drive to see whether it comes back.
Look up TSBs for your vehicle that cover the barometric, MAP or MAF sensor.

Typical fixes

Repair a corroded connector, damaged wiring or poor sensor ground (OBD-Codes.com notes some designs need an added ground, depending on the maker)
Fix a vacuum leak or the engine problem causing low vacuum, such as misfires, a clogged catalytic converter or incorrect timing
Replace the barometric pressure or MAP sensor if it fails testing
Replace a failed MAF sensor where it's the cause (RepairPal)
Correct timing problems, including timing belt replacement where needed (RepairPal lists timing belt replacement as a common repair)
Reprogram or replace the PCM only after everything else checks out

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

OBD-Codes.com recommends a manual engine vacuum test against factory specs: an engine that isn't running efficiently won't make enough vacuum for the MAP or barometric sensor to read correctly.
Test the sensor's resistance on all circuits with a digital volt/ohmmeter against factory specs, and disconnect related controllers before checking circuits to avoid damage. A replacement PCM must be programmed.
On systems where the barometric sensor is part of the MAP sensor, the scan tool may show manifold pressure in place of barometric pressure.
The sources differ in emphasis: RepairPal's list leans toward engine mechanical causes (internal engine failure, timing, vacuum leak) and the MAF sensor, while OBD-Codes.com focuses first on the sensor's connector, wiring and ground before engine vacuum and the PCM.

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0129?

Usually for a short time. RepairPal rates it 'Moderate', so have it diagnosed within a reasonable time. If the engine hesitates badly, misfires or blows black smoke, limit driving until it's fixed.

Is P0129 always a bad sensor?

No. Both sources list wiring and connector problems, and low engine vacuum from wear, misfires, a clogged catalytic converter, timing problems or a vacuum leak can also set it.

Where is the barometric pressure sensor?

It depends on the vehicle. OBD-Codes.com says most makers use a separate sensor mounted away from the engine, often with a vacuum hose, while others build it into the MAP sensor. Check a repair manual for your model.

What codes are related to P0129?

MAP sensor codes P0105 through P0108 and barometric pressure sensor code P2227 involve the same pressure readings.

Sources

Last reviewed 2026-10-26. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.