P0109 Code - Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

What Does P0109 Mean?

OBD-II Code P0109 is defined as a Manifold Absolute Pressure Sensor/Barometric Pressure Circuit Intermittent

The Manifold Absolute Pressure Sensor/Barometric Pressure Sensor measures the rise and fall of the air pressure inside the Intake Manifold. This provides critical data needed for the Powertrain Control Module (PCM) to control the Air Fuel Ratio, the Ignition Spark Timing and many components of the Emission Control Systems.

Code P0109 sets when there is inconsistent or erratic performance in the voltage signal to the PCM from the MAP/Baro Sensor Circuit.

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What are the common causes of P0109 ?

The MAP circuit voltage input to the ECU being too erratic may have several causes:

• The source of the problem is the sensor sending improper voltage information to the ECU.
• The most common problem is a bad MAP sensor.
• The wiring or connector may be bad or have a bad connection or wiring. It could be too close to higher voltage consumption components, especially alternators or ignition wires causing fluctuating voltages. A poor electrical ground can cause problems also.
• The sensor itself may be simply operating out of range from age, fatigue, or damaged parts of the sensor components internally.
• MAP sensors must operate within specific ranges to send correct signals to the ECU. This ensures proper engine operation and smooth power output

What are the symptoms of P0109 ?

Symptoms of a P0109 diagnostic trouble code may include:

• Poor acceleration
• Cherry red hot catalytic converter
• Possible spark knock (detonation / pre-ignition)
• If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected

How do you troubleshoot P0109 ?

NOTE #1: Some applications use MAF (Mass Airflow Sensors) instead of manifold pressure sensors. Moreover, some applications use a barometric sensor that is incorporated into the MAF sensor, with the barometric sensor serving as a back-up to the MAF sensor. In these cases, it is important to inspect the heated element of the MAF sensor for the presence of grime or residues that could impede the performance/accuracy of the sensor. In many cases, a simple cleaning of the element with an approved solvent will cure the problem.

NOTE #2: Before attempting to diagnose code P0109, it is important to ensure that the engine is in perfect running order, with no lean running or misfire conditions present. For instance, unmetered air entering the engine could interfere with the way in which the PCM interprets changes in the manifold pressure/vacuum. Inspect the vacuum system and repair all faults before attempting to diagnose this code. Also, be sure to scan for all trouble codes present, and to repair all other issues found before diagnosing this code.

Step 1

NOTE: In order to make an accurate diagnosis, you will in addition to a suitable code reader and digital multimeter, need a repair manual for the application being worked on to determine the color-coding, location, purpose, and routing of all associated wiring.

Assuming that all other issues had been resolved, record all trouble codes present, and record all available freeze-frame data. This data will be of use if an intermittent fault is identified later on.

Step 2

As a first step in the diagnostic procedure, check for a clogged or dirty air filter element, pinched, damaged, or dislodged vacuum hoses and inlet air ducting, as well as clogged or damaged catalytic converter(s). Repair/replace components and hoses as required.

Operate the vehicle, and rescan the system to see if the code returns.

If however the above components are all in good order, perform a thorough inspection of all wiring and connectors. Repair/replace all burnt, corroded, damaged, or suspect wiring and connectors. Rescan the system to see if the code returns.

Step 3

If the code returns, perform ground, continuity, and reference voltage checks on all wiring at the sensor connector. Be sure to disconnect all control modules before doing continuity checks to prevent damaging the modules, and consult the manual on the color-coding and function of each wire in the connector.

Compare all readings to values stated in the manual, and repair/replace wiring as required. Reconnect all wiring, and operate the vehicle. Rescan the system to see if the code returns.

Step 4

If the code and symptoms persist, consult the manual for the correct test procedure(s) of the MAP/MAF sensor. Be sure to compare obtained readings to the manufacturer’s pressure to Hertz chart. Replace the sensor if any reading(s) fall outside of specified values. Operate the vehicle, and rescan the system to see if the code returns.

NOTE: If the vehicle is fitted with a MAF (Mass Airflow Sensor) instead of a MAP sensor and you have not already done so, now would be a good time to inspect the MAF sensor’s element for residues that could affect its performance. Only use approved solvents to (carefully) clean the element. Reassemble the inlet ducting, operate the vehicle, and rescan the system to see if the code returns.

Step 5

If all obtained readings fall within the manufacturers specifications, it is likely that there is an intermittent fault present, which can sometimes be extremely challenging to locate and repair. If all other repair attempts fail to resolve the problem, you may have to allow the fault to worsen before an accurate and definitive diagnosis/repair can be made.

Although PCM failure is not altogether impossible, it is a rare event. Therefore, the fault must be sought elsewhere before any control module is replaced.

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