What Is the P0129 Code?
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The P0129 code definition is “Barometric Pressure Too Low.” This code happens when the powertrain control module (PCM) or engine control module (ECM) detects a barometric pressure that is lower than specified parameters within your engine. This can occur due to either a reading from the manifold air pressure sensor (MAP sensor, also called the manifold absolute pressure sensor) or barometric pressure sensor (BARO sensor).
More About the P0129 Code
Understanding the air pressure around and inside your vehicle is an important part of running the engine correctly. Your PCM is able to track variations in air pressure and atmospheric pressure, which can change depending on your vehicle’s altitude, through your barometric air pressure sensor (BAP sensor) or BARO sensor, depending on what’s set up in your vehicle. Using these measurements, your vehicle is able to adjust the fuel injection to create the proper air/fuel ratio. This is because as you gain altitude above sea level, the atmosphere gets thinner, and the thinner the atmosphere, the less oxygen is present. With lower O2 levels, the air/fuel charge will also need a lower fuel level. This can be slightly different in vehicles equipped with turbochargers or superchargers, as they both pressurize the intake system in a way that can compensate for altitude changes. This error code indicates that the barometric pressure is exceptionally low, so much so that it could interfere with the general vehicle function.
vehicles equipped with turbochargers or super chargers operate a bit differently with changes in altitude since they both pressurize the intake system that can compensate for altitude changes without a significant change in performance over a naturally aspirated engine.
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What Are the Symptoms of a P0129 Code?
Most of the symptoms of the P0129 error code are issues with fuel delivery and engine performance. You may see excessively rich fuel delivery, which can result in diminished fuel efficiency, hesitation when accelerating, and a general lack of engine performance. In some rare cases, you may see the engine misfire. It is also possible for the exhaust to start emitting black smoke, especially if you have contaminated spark plugs. Even if you don’t see any other symptoms, you should at least see the check engine light turn on with this error code.
What Are Some Causes of a P0129 Code?
There are actually many possible causes of the P0129 code. This code only indicates that one of the sensors that reads actual barometric pressure has indicated a low reading — it doesn’t tell you which sensor or where. That means all of these could possibly be causes of code P0129:
- Faulty manifold air pressure sensor
- Faulty barometric air pressure sensor
- General issues in wiring or connectors
- Issues within the wiring harnesses
- Corroded connector face of sensors
- Clogged catalytic converter
- Insufficient battery ground in sensors
- Dirty air filter element
- Vacuum leaks
- Reference voltage circuit providing improper reference voltage signal
- Other issues in the vehicle, such as reduced fuel pressure
- Defective PCM or PCM programming error, which is unlikely
You’ll need to go through other possible error codes and diagnostic information, including possibly a visual inspection, in order to determine the underlying cause here. This isn’t a cause code but instead a symptom code, so diagnostic trouble code P0129 won’t give you the information you’re looking for.
How Serious Is the P0129 Code?
The P0129 code can be quite serious. Barometric pressure is an important part of air/fuel ratio development, which means that your vehicle may not be able to manage your air/fuel ratio properly without the correct barometric pressure reading. This is on top of the fact that if there are other problems inside your vehicle, those issues can develop into other concerns. You should consider the P0129 code quite seriously.
Can I Still Drive with a P0129 Code?
A P0129 code will not usually prevent you from driving; it’s uncommon for this code to cause your vehicle to stop functioning altogether or to enter Limp Mode or Limp Home Mode. However, if you drive with the P0129 code active, you’re likely to be spending significantly more than you should be on gas, as your fuel consumption will probably rise. Plus, it makes it possible that you could end up experiencing additional problems related to the underlying cause. Instead of just continuing to drive with the P0129 code, talk to an expert about fixing it.
How Easy Is It to Diagnose a P0129 Code?
Diagnosis of the P0129 engine code is often a significantly laborious process. Diagnosis time is often multiple hours, as you’ll need to check various components within your vehicle to determine the underlying problem. It may also require many diagnostic tools, such as a vacuum gauge and digital volt/ohmmeter, as well as technical service bulletins that not all DIYers have access to. Generally, diagnosing the P0129 code is not considered an easy job, and it’s not something that you should do without experience. Instead, talk to a professional about fixing this code.
How Difficult Is It to Inspect a P0129 Code?
Inspection can also be quite difficult. If you look at the list of possible causes, you’ll see many different engine components: you may need to inspect the manifold air pressure sensor, the barometric air pressure sensor, the wiring and connectors to both of these, the connector faces, the catalytic converter, and possibly even the PCM as a whole. You may also need to inspect other sensors, like the crank and cam sensors. Inspecting all of these is often not especially feasible for a DIYer, which is why many DIYers seek expert assistance with this code.
Need Additional Help with Your P0129 Code?
If you need extra help with your code, you’re definitely not alone. This is one of the more complex codes your vehicle can turn up, which means most DIYers will likely have a difficult time handling it by themselves.
If you’re looking for help with a bad MAP sensor or other sensor failure, you should start by finding an auto repair shop in your area. A local repair shop can be very helpful in allowing you to get a fix as easily as possible without having to go too far out of your way.
Additionally, you might want to check out the OBD-Il database at KBB.com before you bring your vehicle in. This database lets you understand more about other codes that your vehicle might also be showing on a diagnostic connector so you can know what repairs may be necessary.
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