P0129 Atmospheric pressure too low

P0129 – OBD-II Trouble Code Technical Description

Atmospheric pressure too low

When it comes to trouble code P0129, barometric pressure plays a crucial role. Low air pressure can be a concern, especially when traveling at high altitudes. Have you noticed this at normal height? What happens when this happens? How can you eliminate the symptoms? Find out everything you need to know about the P0129 code.

What does trouble code P0129 mean?

The first “P” in a diagnostic trouble code (DTC) indicates the system to which the code applies. In this case, it is the transmission system (engine and transmission). The second character “0” indicates that this is a general OBD-II (OBD2) trouble code. The third character “1” indicates a malfunction in the fuel and air metering system, as well as in the auxiliary emission control system. The last two characters “29” represent the specific DTC number.

Error code P0129 means the barometric pressure is too low. This occurs when the powertrain control module (PCM) detects pressure that is below the manufacturer's set value. In other words, the P0129 code occurs when the manifold air pressure (MAP) sensor or barometric air pressure (BAP) sensor is faulty.

How serious is code P0129?

This issue is not critical at this time. However, it is important to regularly check it is up to date and correct it in advance to avoid more serious problems.

*Each car is unique. Features supported by Carly vary by vehicle model, year, hardware, and software. Connect the scanner to the OBD2 port, connect to the application, perform initial diagnostics and check what functions are available for your car. Please also be aware that the information provided on this site is for informational purposes only and should be used at your own risk. Mycarly.com is not responsible for errors or omissions or for the results obtained from the use of this information.

Since this problem can cause the engine to misfire and exhaust gases to enter the vehicle's interior, it is important to fix it as soon as the above symptoms appear.

What are the symptoms of code P0129

You may suspect this error code if you notice the following symptoms:

1. Check if the engine light is on.
2. Noticeably high fuel consumption.
3. Poor engine performance.
4. Engine misfiring.
5. Fluctuations in engine operation during acceleration.
6. The exhaust emits black smoke.

Reasons for code P0129

Possible causes for this code include:

1. Corroded MAF/BPS sensor connector surface.
2. Insufficient engine vacuum due to engine wear, misfire or clogged catalytic converter.
3. Faulty BPS (manifold air pressure sensor).
4. Open or shorted MAP and/or BPS sensor wiring.
5. Insufficient system grounding at MAF/BPS.
6. Faulty PCM (engine control module) or PCM programming error.
7. Malfunction of the manifold air pressure sensor.
8. The barometric air pressure sensor is faulty.
9. Problems with wiring or connectors.
10. Corrosion on the connector surface of any of the sensors.
11. Clogged catalytic converter.
12. Lack of system grounding on the sensors.

PCM and BAP sensor

Atmospheric pressure varies in proportion to altitude above sea level. The barometric air pressure (BAP) sensor plays an important role in allowing the engine control module (PCM) to monitor these changes. The PCM uses information from the BAP to regulate the amount of fuel delivered and when the engine starts.

Moreover, the reference voltage, battery ground, and one or more output signal circuits are routed to the barometric pressure sensor. The BAP adjusts the voltage reference circuit and changes the resistance according to the current barometric pressure.

When your vehicle is at high altitude, the barometric pressure automatically changes and therefore the resistance levels in the BAP change, which affects the voltage sent to the PCM. If the PCM detects that the voltage signal from the BAP is too low, it will cause the P0129 code to appear.

How to diagnose and fix the P0129 code?

The solution to the P0129 code can vary greatly depending on the vehicle manufacturer, as the specifications of the BAP and MAP sensors can vary significantly. For example, the methods for troubleshooting P0129 on a Hyundai may not be appropriate for a Lexus.

To successfully diagnose the error, you will need a scanner, a digital volt/ohmmeter and a vacuum gauge. Following these steps will help you diagnose and determine the necessary repair procedures:

1. Start with a visual inspection to identify damaged wiring and connectors. Any damage found should be repaired before further diagnosis.
2. Since low battery voltage can cause P0129, check the battery capacity and terminal condition.
3. Write down all codes to ensure that the problem is only with the mentioned sensors and system, eliminating other possible problems.
4. Perform a vacuum check of the engine. Keep in mind that previous engine drain problems such as stuck catalytic converters, restrictive exhaust systems, and low fuel pressure can also affect engine vacuum.
5. If all sensors and circuits are within manufacturer specifications, suspect a faulty PCM or PCM software.
6. Any damage found in the wiring and connectors should be repaired.

Following these steps will help you effectively diagnose and resolve the P0129 error code problem on your vehicle.

How much does it cost to fix code P0129?

Identifying the P0129 error code can be quite a time-consuming process and typically costs between 75 and 150 euros per hour. However, labor costs may vary depending on the location and make of your vehicle.

Can you fix the code yourself?

It is always better to seek professional help as solving the problem requires a certain level of technical knowledge. This is also because the error code is sometimes accompanied by many other trouble codes. However, if you experience any symptoms, you can always get diagnosed and seek early help.

What is P0129 Engine Code [Quick Guide]