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  • If your vehicle logs a P0109 trouble code, it typically means that the powertrain control module (PMC) has detected an intermittent sensor reading from the MAP or BARO sensor circuit.
  • Aside from a faulty MAP or BARO sensor, corroded, loose, or damaged wiring can cause onboard diagnostics to log a P0109 code.
  • If this code is present, your vehicle might exhibit symptoms like hesitation, decreased engine performance, and poor fuel economy.

P0109 is one of the several engine trouble codes related to a possible fault in the manifold absolute pressure (MAP) or barometric pressure (BARO) sensor circuit.

What Does the P0109 Code Mean?

Diagnostic trouble code (DTC) P0109 stands for “MAP/BARO Sensor Circuit Intermittent.” It is triggered when a vehicle’s PCM has detected a possible issue in the MAP sensor or BARO sensor circuit. The error code is specifically logged once the PCM perceives an intermittent sensor reading from either the MAP or BARO sensor.

See also  P0069 Code: Manifold Absolute Pressure - Barometric Pressure Correlation
man using scan tool to diagnose obd code
Code P0109 is triggered when a vehicle’s PCM has detected a possible issue in the MAP sensor or BARO sensor circuit.

A MAP sensor is used to monitor engine load. Some vehicles may be equipped with a MAP sensor and a separate BARO sensor. A BARO sensor is similar to a MAP sensor, but it can detect more minute or subtle changes in atmospheric air pressure.

The two sensors typically refer to the same type of sensor. The only difference is that a MAP sensor is usually connected to the manifold, while a BARO sensor is vented directly to the atmosphere. The two sensors are often integrated into a single sensor.

A MAP sensor is usually supplied with a reference voltage signal, a battery ground, and one or several output signal circuits. This sensor’s resistance level is expected to change as absolute manifold pressure changes. These changes will cause variations in the output voltage signal sent to the PCM.

This data is not only used by the PCM to detect engine load but also to adjust fuel injection and ignition timing.

Once the PCM detects that the input voltage is outside the manufacturer-specified range for a given amount of time, it will trigger the engine code P0109.

A detailed understanding of intake manifold pressure can help you perform a proper DIY diagnosis and troubleshooting of code P0109.

Note: The definition of code P0109 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What Are the Possible Causes of the P0109 Code?

Here are the possible triggers of the P0109 code:

  • Faulty MAP sensor
  • Open or shorted MAP or BARO circuit
  • Malfunctioning BARO sensor
  • Corroded or loose MAP/ Baro sensor connector
  • Malfunctioning PCM
See also  P0106 Code: Manifold Absolute Pressure/BARO Sensor Range/Performance

What are the Common Symptoms of a P0109 Code?

Here are the common symptoms of a P0109 code:

car with increased fuel consumption
Increased fuel consumption is a symptom of code P0109.

How to Diagnose the P0109 Code

It’s not easy to diagnose a P0109 code. If you don’t have the right tools and experience for this task, it is best to let a mechanic do the diagnostic procedures for you.

However, if you’re an experienced DIYer, and you would like to try and diagnose this code yourself, we recommend consulting vehicle-specific repair manuals and/or online repair databases. These sources can help you identify the right diagnostic procedure for your vehicle.

How to Fix the P0109 Code

Although the symptoms and causes of this error code may be similar in various makes and models, there is no single fix that would work for all vehicles.

Remember that vehicle engines are designed and built differently by each vehicle manufacturer. This means that the appropriate repair procedures may vary per vehicle. For instance, a P0109 Ford code fix may not resolve a code P0109 on a Chevy.

See also  P0129 Code: Barometric Pressure Too Low

Consult a vehicle repair manual before attempting to clear this code yourself. You may also subscribe to an online repair database to help you find confirmed fixes for your vehicle.

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About The Authors
Richard McCuistian, ASE Certified Master Automobile Technician
Reviewed By Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

CarParts Research Team
Written By Research Team

Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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