P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
OBD-II Trouble Code Technical Description
Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to all 1996-newer vehicles (Ford, Hyundai, Kia, Mazda, Mercedes Benz, etc.). Although generic, the specific repair steps may vary depending on make/model.
When I discover that a P0109 code has been stored, I know that it means that the powertrain control module (PCM) has detected an intermittent manifold absolute pressure/barometric pressure reading from the manifold absolute pressure sensor (MAP) or the barometric pressure sensor (BPS).
The MAP sensor is designed to enable the PCM to monitor variations in atmospheric pressure using absolute intake manifold pressure. Atmospheric pressure is directly related to the particular degree of altitude, as it applies to your vehicle. The MAP sensor is usually supplied with a reference voltage (5-volt) signal, a battery ground, and one (or more) output signal circuit/s.
MAP sensor resistance levels react to changes in absolute manifold pressure. Changing resistance levels in the MAP sensor create variations in sensor output voltage to the PCM. These varying voltage signals are not only used by the PCM to calaculate fuel delivery and ignition timing, but also compared with programmed specifications.
If input voltage fails to comply with programmed specifications, under certain circumstances for a set period of time, a P0109 will be stored and a malfunction indicator lamp (MIL) may be illuminated.
There are several different system of monitoring manifold absolute/barometric pressure. Consult your vehicle service manual or All Data (DIY) to determine the exact MAP sensor design of your vehicle.
An example of a MAP sensor
Several manufacturers use a MAP sensor and a separate barometric pressure sensor. In this case, the MAP sensor is mounted away from the engine and has a vacuum hose connected to it. The degree of engine intake vacuum is gathered by the sensor and input to the PCM, where it is compared with the input signal from the barometric pressure sensor, intake air temperature, and other factors to determine actual altitude (elevation above sea level). If the MAP sensor and BPS input signals vary by more than the specified degree, a P0109 will be stored and a MIL illuminated.
Most automakers integrate the MAP sensor with the BPS. In this type of system, the sensor is mounted to the engine intake manifold. The scanner data stream may reflect only manifold absolute pressure instead of MAP and barometric pressure for this type of system.
Severity & Symptoms
Since the conditions that cause a P0109 to be stored will likely lead to very poor fuel efficiency and engine drivability issues, this code should be addressed urgently.
Symptoms of a P0109 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
Tools that I would likely use to diagnose a P0109 are a diagnostic scanner, a digital volt/ohmmeter, a vacuum gauge, and a vehicle service manual (or online service such as All Data DIY).
I like to begin my diagnosis with a visual inspection of system related wiring harnesses and connectors. Corroded connector faces and damaged wiring must be rectified before proceeding with the diagnostic process.
Connect the scanner to the diagnostic connector and retrieve all stored codes and freeze frame data. Make a note of this information. It may prove useful in the event that the P0109 is an intermittent code. Clear the codes and test drive the vehicle.
An engine vacuum test can help to ensure that the engine is making sufficient vacuum. Consult your vehicle information source for minimum engine vacuum specifications. Poorly running engines will not produce sufficient vacuum for the MAP sensor. Ignition misfire codes should be diagnosed and repaired before attempting to diagnose a P0109. Clogged catalytic converters, restricted mufflers, and low fuel pressure may also contribute to insufficient engine vacuum.
If a P0109 is immediately reset, and all circuits and connectors appear to be in order, continue testing at the MAP sensor. Follow manufacturer’s recommendations for testing the MAP sensor. Use the DVOM to test resistance of the MAP sensor. If the MAP sensor fails to comply with resistance specifications, replace it. To prevent damage to related controllers, disconnect them before testing resistance levels in system circuits with the DVOM. Repair or replace open or shorted circuits as required.
Suspect a defective PCM or a PCM programming error if the sensor and all circuits are compliant with manufacturer’s specifications.
Other MAP Sensor engine codes include P0105, P0106, P0107, and P0108.
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"Delete Error Code Permanently, Disable DTC Error Code Function for p0109 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p0109 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0109.
