P0105 OBD-II: Manifold Absolute Pressure/Barometric Pressure Circuit

What Does P0105 Code Mean?

OBD-II Code P0105 is defined as a Manifold Absolute Pressure Sensor/Barometric Pressure Circuit Malfunction

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, Ignition Spark Timing, and many components of the Emissions Control Systems. The Manifold Absolute Pressure/Barometric Pressure Sensor converts the Intake Manifold air pressure into a voltage that is high when the Intake Manifold air pressure is high and low when the Intake Manifold air pressure drops to a vacuum.

Code P0105 sets when the output voltage stays less than .5 volts or above 4.5 volts for several seconds when there is changing rpm and throttle position values

P0105 Symptoms

• Check Engine Light will illuminate
• In some cases, the engine may be hard starting and/or get poor fuel economy
• In some cases, noticeably poor engine performance may occur

Common Problems That Trigger the P0105 Code

• Manifold Absolute Pressure Sensor/Barometric Pressure Sensor is defective
• Intake Manifold vacuum leaks
• Faulty or corroded Manifold Absolute Pressure Sensor/Barometric Pressure wiring or connections

Common Misdiagnoses

• Manifold Absolute Pressure Sensor/Barometric Pressure Sensor is replaced when the real cause is an Intake Manifold vacuum leak
• Manifold Absolute Pressure Sensor/Barometric Pressure Sensor is replaced when the real cause is a stuck-open EGR Valve
• Manifold Absolute Pressure Sensor/Barometric Pressure Sensor is replaced when the real problem is a defective Idle Air Control Motor, which causes a very low engine idle

Polluting Gases Expelled

• HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
• CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
• NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

P0105 Diagnostic Theory for Shops and Technicians

When diagnosing a P0105 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive while paying close attention to engine load, throttle position, RPM, and road speed with a data streaming scan tool. As you drive the vehicle, compare these values to the MAP Sensor PID or parameter ID. The MAP Sensor voltage values should rise and fall with changes in engine speed and engine load. Typically the values will vary from 4 volts or more when accelerating and to 1 volt or less when decelerating.

Check the MAP sensor connector with the key on and the engine off. There needs to be a steady 5 volt reference voltage and a very good ground. The third wire will be the MAP Sensor signal wire which sends data to the Power Train Control Module. Find and use the proper engine performance wiring diagram to discern the proper color and position of these wire in the connector.

It never hurts to do a vacuum pump voltage output test of the MAP sensor. You can watch the output on the scan tool. The voltage should steadily decrease from 5 volts to less than .5 volts as you apply 18-20 inches of vacuum. I also like to wiggle the MAP sensor wiring harness as I apply vacuum to ensure that the MAP sensor wiring and/or connector aren't contributing to the problem. Always inspect the vacuum hose and if the MAP sensor plugs directly into the intake manifold, be sure to check its seal, as they can split and cause erratic readings.