P0105
PowertrainManifold Absolute Pressure/Barometric Pressure Circuit Malfunction
The ECU has spotted an electrical problem in the manifold absolute pressure sensor circuit, the sensor that tells the engine how much air is going into the manifold. The engine uses that reading to work out fuelling, so when the signal goes missing or reads nonsense, the fuel delivery goes off and you'll usually feel it. On turbo and supercharged engines this sensor is doing extra work measuring boost pressure, so a fault here can also drop the car into limp mode to protect the engine.
ⓘ Information only. This page provides general educational information about fault code P0105. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0105 mean?
P0105 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, often the first thing you notice
- • Rough or lumpy idle, sometimes hunting up and down
- • Flat spot or hesitation when you put your foot down, particularly off boost
- • Fuel economy noticeably worse, especially around town
- • Harder starting from cold
- • On turbo cars, the engine dropping into limp mode and refusing to make boost
Possible causes
Causes commonly associated with P0105, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Faulty MAP sensor itself, the most common cause. These cook over time sat in a hot boost pipe or on the manifold
- 2. Damaged or corroded wiring to the sensor. Look for chafed looms and green crud in the connector, common where the loom runs near hot pipework
- 3. A split or disconnected vacuum hose feeding the sensor, or a boost leak on turbo engines
- 4. Poor or loose connection at the sensor plug, sometimes just a clip that's worked loose with vibration
- 5. Problem with the 5-volt reference feed from the ECU, which kills or pins the signal
- 6. Faulty throttle position sensor confusing the picture by feeding the ECU inconsistent throttle data
- 7. Failed ECU. Rare, and only worth considering once everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the freeze frame data and see what the engine was doing when the code logged. Cold start, on boost, or idling all point in different directions
- 2. Get under the bonnet and check the sensor connector for corrosion, bent pins, and a loose clip. Wiggle the loom with the engine running and watch for the reading to drop out
- 3. Inspect the vacuum hose to the sensor and, on turbo cars, the boost pipes and clamps for splits or oil weeping that gives away a leak
- 4. Back-probe the signal wire with the ignition on and engine off. At sea level you want roughly 4 to 4.5 volts on a typical MAP sensor
- 5. Take it for a drive watching live MAP data. The reading should climb smoothly with throttle and boost. Flatlines, spikes, or numbers that don't move are the giveaway
- 6. Check the 5-volt reference and the ground at the plug with a multimeter. No reference voltage means a wiring or ECU fault rather than a duff sensor
Common questions about P0105
Can I keep driving with a P0105, or should I leave the car parked? +
Short trips to get it looked at are usually fine, but don't make a habit of it. The engine is fuelling off a bad or missing air reading, so it may run rich, idle badly, and on a turbo or supercharged car it'll often sit in limp mode with no boost. That won't strand you but it makes for slow, thirsty driving. If the warning light is flashing rather than steady, stop driving, that points to a misfire that can wreck the cat.
Is this going to fail the MOT? +
The code on its own isn't a direct MOT failure, but the engine warning light is. If the MIL is lit when the tester plugs in or eyeballs the dash, it's a fail on that alone. A car running rich with this fault can also fall down on the emissions check. Sort the fault, clear the light, drive a few cycles so it stays off, then book the test.
What's it likely to cost to put right? +
Depends entirely on the cause. A split vacuum hose or a clean-up of a corroded connector is low two figures, sometimes nothing if you do it yourself. A new MAP sensor fitted at an independent garage usually runs £80 to £180 all in, the part itself often £25 to £70. Wiring repairs are harder to price because it's labour to chase the fault. A main dealer will charge a fair bit more on labour for the same job.
How do I tell whether it's the sensor or just a wiring or hose problem? +
Start with the cheap stuff. If the vacuum hose or boost pipe is split, you'll often hear or see it, and patching that may clear the code on its own. With a multimeter, check you've got the 5-volt reference at the plug. If the reference is missing or the ground is bad, you've got a wiring or ECU issue, not a dead sensor. If the reference is good and the signal voltage is stuck or jumpy with the engine running, the sensor is the culprit. Swapping in a known-good sensor is the quickest confirmation if you can borrow one.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →