Modern vehicles are equipped with on-board diagnostic (OBD) systems that help you or a mechanic determine what’s causing certain issues in your vehicle. Your car’s check engine light will usually illuminate once the powertrain control module (PCM) detects a problem with any engine component. If you have a scan tool with you, you may connect it to your vehicle’s OBD port to retrieve the specific error code.
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.
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.
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
What are the Common Symptoms of a P0109 Code?
Here are the common symptoms of a P0109 code:
- Illuminated check engine light
- Engine hesitation (during acceleration)
- Decreased engine performance
- Increased fuel consumption
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.
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.