P0105 Code: Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction

What the P0105 code means

The manifold absolute pressure (MAP) sensor measures the vacuum the engine creates as it draws air in, and from that reading the computer works out how much air is entering so it can calculate fuel injection. On many vehicles the same sensor also measures barometric pressure when you turn the key on, which lets the computer correct for altitude.

The P0105 code is the general code for that circuit. It says something is not working as it should without saying what. P0106 specifies that the value is outside what is expected, P0107 that the signal is too low and P0108 that it is too high.

That hierarchy organizes the work. If P0105 shows up alone, the system detected an anomaly it could not classify and you need to check the whole circuit. If it shows up with one of the others, start with the specific one.

The causes repeat across all of them: the sensor hose on remote-mounted sensors, the connector, vacuum leaks that change the real pressure, and carbon buildup at the manifold port. A truly failed sensor is less common than people assume.

It helps to see why this reading is so central to engine management. The airflow entering the engine determines how much fuel to inject, and on vehicles with no air flow sensor that airflow is calculated precisely from manifold pressure, engine speed and temperature. That makes the MAP sensor the basis of the whole calculation: if its reading drifts, injection, spark advance and transmission shift strategy drift with it.

The dual role of this sensor on many vehicles is worth knowing. When you turn the key on, before starting, it measures the atmospheric pressure where you are and the computer stores that value as the barometric reference. From then on, every later measurement is read as a difference from that reference.

That has a practical consequence: if the sensor reads wrong at that first instant, all later engine management starts from the wrong reference even if the sensor works fine afterward. It also explains why, on vehicles that often change altitude, you should check the key-on reading at every diagnosis.

P0105 code symptoms

• Check engine light on.
• Unstable idle, or an engine that stalls when you come to a stop.
• Hesitation and lack of response when you accelerate.
• Higher fuel use.
• Hard starting.
• Black smoke if the computer enriches the mixture too much.
• Loss of power on hills.
• May appear together with a P0106, P0107 or P0108.
• Performance gets worse after big changes in altitude.

Likely causes of the P0105 code

1. Sensor hose cracked, loose or clogged on remote-mounted sensors.
2. Vacuum leaks in hoses, the manifold gasket, the PCV valve or the brake booster.
3. Connector corroded, wet or with backed-out pins.
4. Manifold pressure port clogged with carbon.
5. Wiring damaged by heat or rubbing.
6. Sensor ground with high resistance.
7. Five volt reference missing or unstable.
8. Failed or out-of-calibration sensor.
9. Sensor gasket missing or misplaced.
10. Wrong barometric reading at key on, which leaves all later engine management working from the wrong reference.

How to diagnose the P0105 code step by step

1. Check the reading with the key on and the engine off. It should show the atmospheric pressure where you are.
2. Watch the value at warm idle. A healthy engine reads between 25 and 40 kilopascals (about 7 to 12 inHg).
3. Inspect the sensor hose if it is mounted remotely. Cracks, kinks and clogs are common.
4. Smoke test the intake to locate vacuum leaks.
5. Clean the pressure port on the manifold if there is carbon.
6. Check power, ground and signal at the connector.
7. Wiggle the harness with the key on and watch the reading.
8. Check whether more specific codes are stored for the same circuit, which would narrow the diagnosis.
9. Check the reading right at key on, before starting. That is the moment the system takes its barometric reference.

How to fix the P0105 code

• Replace the sensor hose if it is cracked, crushed or clogged.
• Repair the vacuum leaks you find and replace the PCV valve if it is stuck.
• Clean the manifold pressure port and the sensor itself with a product made for that.
• Clean or replace the corroded connector and protect it with dielectric grease.
• Repair the damaged wiring and correct the sensor ground.
• Seat the gasket correctly when you install the sensor.
• Replace the sensor if, with a sealed intake and a good circuit, it still reads wrong.
• After the repair, verify that the key-on reading matches the atmospheric pressure at your altitude.

Technical reference data

• Pressure with the key on and the engine off: atmospheric, about 101 kPa (14.7 psi) at sea level.
• Pressure at warm idle: between 25 and 40 kPa on a healthy naturally aspirated engine.
• Typical signal: 0.5 to 4.5 volts, or a frequency signal depending on the type.
• 5 volt supply with its own ground.
• Altitude lowers atmospheric pressure: at 2,200 meters (about 7,200 feet) it is around 78 kPa (11.3 psi).
• P0106 specifies range, P0107 low signal and P0108 high signal.
• Many vehicles use this sensor to take the barometric reference at key on, before starting.

Brand-specific notes

With a P0105 code in a high-altitude city, remember the reference values change. A sensor that reads 78 kilopascals with the engine off is not bad if you are at 2,200 meters (about 7,200 feet). It is correctly measuring the atmospheric pressure where you are.

On remote-mounted sensors, the hose is as suspect as the sensor itself and much cheaper. Check all of it before you buy anything, paying attention to hardened ends.

Frequently asked questions about P0105