Skip to content

P0109 – Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent (OBD2)

P0109 means "Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent". The manifold absolute pressure (MAP) sensor signal briefly drops out or jumps. The fault comes and goes – often with vibration, heat or moisture – so the part may test fine in the workshop.

Last updated

P0109 quick summary

Fault codeP0109
MeaningManifold Absolute Pressure/Barometric Pressure Circuit Intermittent
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityMedium
Can I drive?Usually yes, gently. The engine runs on substitute values, so power and economy suffer and turbo engines may go into limp mode. Have it checked soon.
Repair cost€25 – €250

How the MAP and barometric pressure sensors work

The MAP sensor measures the absolute pressure in the intake manifold, which tells the engine control unit how much load the engine is under and, on turbo engines, how much boost there is.

The manifold absolute pressure sensor is a small sensor on or near the intake manifold, often combined with an intake air temperature sensor. It has three wires: 5 V reference, ground and signal. On naturally aspirated engines the pressure is lowest at idle (strong vacuum) and rises towards atmospheric pressure at full throttle; on turbo engines it continues to rise above atmospheric pressure as boost builds.

Many engines also have a barometric pressure sensor – either separate, built into the engine control unit, or read from the MAP sensor with the engine off. The control unit uses atmospheric pressure to correct fuelling and boost at altitude. Codes such as P0068 and P0069 compare these readings with the throttle position or the MAF value; when they do not agree, the engine cannot be sure how much air it is getting.

Because the MAP signal is used to calculate injection quantity and ignition timing, a faulty reading causes poor running, high fuel consumption and – on turbo engines – incorrect boost control or limp mode.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16493 (P0109). Both numbers mean the same fault.

Symptoms of P0109

  • Check Engine light on
  • Hesitation, poor acceleration or limp mode (turbo engines)
  • Rough idle or stalling
  • Higher fuel consumption, black smoke on diesels
  • Hard starting

Most common causes of P0109 (most likely first)

Mechanic's Pro Tip

On diesels and direct-injection petrol engines, a MAP sensor clogged with oily soot is far more common than an electrically failed one. Pull the sensor out and look at the tip before ordering a new one – a careful clean with electrical contact cleaner often fixes the problem.

  1. 1.Loose or corroded connector pin

    Most likely

    Pins that have spread lose contact as the engine vibrates.

  2. 2.Chafed wire that shorts only now and then

    Often where the harness moves with the engine.

  3. 3.Internal intermittent fault in the manifold absolute pressure (MAP) sensor

  4. 4.Cracked or disconnected vacuum hose to the sensor

    On sensors connected by a hose, a split hose makes the reading wrong; on directly mounted sensors a damaged O-ring does the same.

  5. 5.Sensor port blocked with oil or soot

    Oil mist from the crankcase ventilation and EGR soot can clog the small sensor opening – very common on diesels.

  6. 6.Faulty MAP or barometric sensor

    The sensing element drifts or fails internally.

  7. 7.Intake or boost leak

    A real leak changes the measured pressure and can set range/performance or correlation codes.

Step-by-step diagnostic guide

  1. 1

    Read codes and compare with related sensors

    Read all fault codes. Check for related throttle, MAF, boost or reference voltage codes, which point to the real cause.

  2. 2

    Do a wiggle test

    With the engine running and the manifold absolute pressure (MAP) sensor value in live data, gently move the harness and connector. If the value jumps or the code returns, the fault is in that section. Also check pin tension with a matching terminal.

  3. 3

    Check key-on, engine-off reading

    With the ignition on and the engine off, the MAP and barometric readings should both equal the current atmospheric pressure (about 1,000 mbar / 100 kPa at sea level, less at altitude). A large difference between them points to the sensor.

    Multimeter: Key on, engine off: MAP ≈ barometric pressure ≈ 950–1,030 mbar near sea level. Warm idle on a naturally aspirated engine: about 300–400 mbar absolute.

  4. 4

    Inspect hoses, O-rings and the sensor port

    Remove the sensor and check the O-ring and the opening for oil or soot. Check any vacuum hose for cracks and correct routing.

  5. 5

    Check reference, ground and signal

    Measure the 5 V reference and ground at the connector and watch the signal change smoothly when revving the engine or applying vacuum with a hand pump.

  6. 6

    Clean or replace and re-test

    Clean a sooted sensor port carefully, replace the sensor if its readings are wrong, clear codes and confirm normal values on a test drive.

Frequently asked questions

Can I keep driving with P0109?

Usually yes, gently. The engine runs on substitute values, so power and economy suffer and turbo engines may go into limp mode. Have it checked soon.

How much does it cost to fix P0109?

Typical repair costs are 25 € – 250 €, depending on the cause and the vehicle. The most common fixes are: loose or corroded connector pin; chafed wire that shorts only now and then; internal intermittent fault in the manifold absolute pressure (MAP) sensor. Always confirm the cause with the tests above before buying parts.

What is the difference between a MAP and a MAF sensor?

A MAF sensor measures the mass of air flowing into the engine, while a MAP sensor measures the pressure in the intake manifold. Some engines use both, some only one. Both values are used to calculate how much fuel to inject.

Can a vacuum leak cause a MAP sensor code?

Yes. A real vacuum or boost leak changes the pressure the sensor sees, so range/performance or correlation codes can appear even though the sensor itself is fine.

What is the difference between P0109 and similar codes?

P0109 belongs to a group of codes for the same component that differ in the type or location of the fault: P0106 – Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem; P0107 – Manifold Absolute Pressure/Barometric Pressure Circuit Low Input; P0108 – Manifold Absolute Pressure/Barometric Pressure Circuit High Input; P0129 – Barometric Pressure Too Low; P2227 – Barometric Pressure Sensor Range/Performance; P2228 – Barometric Pressure Sensor Circuit Low. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.