P0129 Barometric pressure reading lower than the engine computer expects

Barometric pressure too low

Severity not verified — if the car runs badly, have it inspected

The code reports a low barometric pressure reading, which the computer uses to adjust fuel and ignition. No source read for this file grades the risk, but owner complaints link it to stalling, so treat a stall as a reason to get it checked promptly.

It gets more serious if:

  • Inspect soon: Get it inspected soon if the engine stalls while driving or at a stop. Two owner complaints on 2007 and 2009 Jeep Grand Cherokees describe stalling with P0129 stored.

Source: how we rate severity

P0129 in short

P0129 means the engine computer read a barometric pressure that was too low. It takes that reading from a barometric sensor or the manifold pressure sensor. A faulty sensor, wiring or connector problem is the usual cause. Hesitation and poor fuel economy are common, and owners also report stalling.

The computer needs to know the outside air pressure, which falls with altitude, to set fuel delivery and ignition timing. TroubleCodes.net says P0129 sets when the computer sees a low barometric reading from the barometric pressure sensor or the manifold pressure sensor.

On many engines there is no separate barometric sensor, and the computer takes a baro reading from the manifold pressure sensor with the key on before starting. A weak signal from that sensor can then set the code.

Owner complaints on Jeep Grand Cherokee and Dodge Neon describe P0129 as barometric pressure, sometimes with a stall.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Manifold pressure or barometric pressure sensor fault

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a defective MAP or barometric sensor first, and these are the sensors the code is read from.
    What would change this
    Rises if the sensor reading with the key on and engine off is clearly off for your altitude. Falls if it reads normally.

  2. Open or shorted wiring, corroded connector or poor ground

    Common general cause
    Why it ranks here
    The same source lists wiring faults, corroded connector faces and insufficient grounding as common causes.
    What would change this
    Rises if the reading changes when the harness or connector is moved. Falls if the circuit tests sound.

  3. Engine computer fault or programming error

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists a computer malfunction or programming error, ranked last.
    What would change this
    Rises only after the sensor and wiring are cleared. Falls if a replacement sensor and a sound circuit fix the code.
    How to test the engine control module (ecm / pcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data with a scan tool. Note any manifold pressure codes stored with P0129.

    Low riskTool: OBD-II scan tool

    • IfA manifold pressure code such as P0107 or P0108 is stored as well

      It meansThe same pressure sensor circuit is suspect.

      Go to step 2

    • IfP0129 is alone

      It meansCheck the pressure reading live.

      Go to step 2

  2. With the key on and the engine off, read the manifold or barometric pressure on a scan tool and compare it with the normal outside pressure for your altitude.

    Low riskTool: scan tool with live data

Symptoms

  • Check engine light on
  • Hesitation when accelerating and poor fuel economy
  • Black exhaust smoke from a rich mixture
  • Engine stalls at a stop or while driving Gets more serious: stop and have it checked.

How to fix

  1. With the engine off, look at the pressure sensor connector for corrosion or a loose fit.

On your vehicle

Jeep

  • 2007–2009 · Grand Cherokee

    Supported by vehicle data

    Owner complaints (ODI 10496081, 10551947, 10567604) report P0129 stored with stalling on 2007 and 2009 Grand Cherokees, one describing it as barometric pressure out of range; a dealer checked the MAP sensor and found it fine. Complaint signal only.

Dodge

  • 2005 · Neon

    Supported by vehicle data

    An owner complaint (ODI 10321868) reports P0129 as barometric pressure after the car stalled. One owner report only.

  • P0107Manifold pressure or barometric pressure sensor signal too low

    Same system Possible — needs testing

    P0107 is the low-signal code for the manifold pressure sensor that also supplies the barometric reading on many engines.

All Air metering (MAF, MAP and intake air temperature) codes

P0129 questions

What does P0129 mean?

The engine computer read barometric pressure lower than expected, from a barometric sensor or the manifold pressure sensor.

Does a low barometric reading mean I am driving at altitude?

Altitude lowers the real pressure, but a normal reading for your altitude should not set the code. A reading well below it points to the sensor or its circuit.

Sources and review

  1. P0119, P00B7 and P0129 trouble code pages — TroubleCodes.net
  2. NHTSA owner complaints naming P0119 (ODI 10484858, 10714028), P0129 (ODI 10321868, 10496081, 10551947, 10567604) and P00B7 (ODI 11561868, 11575521, 11756349, 11768539) — NHTSA Office of Defects Investigation
Last reviewed
Written by
Saurabh K.
Editorial review
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Technician review
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