P0129 Code - Barometric Pressure Out Of Range Low

Discussion in 'P - Powetrain Codes' started by fault code, Dec 9, 2017.

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    fault code Administrator Staff Member

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    What Does P0129 Mean?

    OBD-II Code P0129 is defined as a Barometric Pressure Too Low

    The engine control module (PCM) uses a Pressure sensor in the intake to determine airflow through the engine. If the PCM detects the signal is too low, it will set code P0129.

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    What are the common causes of P0129 ?
    • Faulty Manifold Absolute Pressure (MAP) sensor
    • Manifold Absolute Pressure (MAP) sensor harness open or shorted
    • Manifold Absolute Pressure (MAP) sensor circuit poor electrical connection
    What are the symptoms of P0129 ?

    Symptoms of a P0129 code may include:
    • Excessively rich fuel delivery conditions
    • General lack of engine performance
    • Hesitation upon acceleration
    • Black smoke from exhaust
    • Diminished fuel efficiency
    How do you troubleshoot P0129 ?

    A diagnostic scanner, a digital volt/ohmmeter, a vacuum gauge, and a vehicle service manual (or online service such as All Data or Mitchell On Demand) will be required to correctly diagnose a P0129.

    I normally begin my diagnosis with a visual inspection of any system related wiring harnesses and connectors that I can gain access to in a reasonable amount of time. Damaged wiring or corroded connector faces must be repaired before continuing the diagnostic process.

    This is a good time to check battery voltage capacity and alternator output. Check battery terminal ends for excessive corrosion. Clean and tighten terminal ends as required. Addressing this issue (now) may save some time if P0129 has been stored due to a low battery voltage or voltage drop condition.

    Connect the scanner to the diagnostic connector and retrieve all stored codes. Make a note of all codes and freeze frame data as this information may prove useful in the event that you are dealing with an intermittent code.

    vacuum-gauge.jpg

    Perform an engine vacuum test to ensure that the engine is making sufficient vacuum. Consult the service manual or information service to obtain specifications that apply to your vehicle. Engines that are not performing efficiently will not produce sufficient vacuum to the BPS or MAP sensor. Engine misfire codes should be diagnosed and repaired before attempting to diagnose this code. Conditions such as clogged catalytic converters, restricted mufflers, and low fuel pressure may also contribute to a loss of engine vacuum.

    corroded-maf-connector-300x225.jpg

    In my personal experience, barometric pressure sensors that are integrated with the MAF sensor are subject to corrosion at the connector face. These types of systems are also subject to malfunctions caused by an extremely dirty air filter element. In addition to these proclivities, this type of BPS configurations will often require that an auxiliary ground be installed. Consult the service manual or information service for technical service bulletins that apply to the barometric pressure sensor, manifold air pressure sensor, or mass air flow sensor of your vehicle.

    If all circuits and connectors appear to be in order, continue testing at the MAP/BPS sensor/s. Consult the service manual for exact specifications pertaining to your vehicle. Unplug the electrical connector and check resistance across all circuits, using the DVOM. Replace the sensor if it fails to comply with specifications.

    If the sensor meets manufacturer’s requirements, begin testing system circuits. Make sure that system reference voltage and ground signals are present. Before testing system circuits with the DVOM, disconnect all related controllers to prevent damage. Repair or replace open or shorted circuits as necessary.

    If the sensor and all circuits are compliant with manufacturer’s specifications, suspect a defective PCM or a PCM programming error. Consider all manufacturer’s recalls and TSBs before replacement and remember that replacement of system controllers will require reprogramming.

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