P0109🔧 Air intake / manifold absolute pressure (MAP) sensorDrive with caution, fix soon

P0109: MAP/Barometric Pressure Circuit Intermittent (Meaning, Causes, Fixes)

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0109 means

The MAP sensor measures the rise and fall of air pressure inside the intake manifold and sends the PCM a voltage it uses to set fuel delivery, ignition timing and several emissions systems. It is fed a 5-volt reference and a ground and returns a signal. P0109 is the intermittent code in the MAP set: RepairPal says it sets when the voltage signal from the MAP/baro sensor circuit is inconsistent or erratic, and OBD-Codes.com says it sets when the signal fails to match programmed specifications under certain conditions for a set period of time. It is a generic code for 1996 and newer OBD-II vehicles, and the repair steps vary by make and model. OBD-Codes.com explains that most automakers build the barometric sensor into the MAP sensor on the intake manifold, but some use a separate MAP sensor (mounted away from the engine on a vacuum hose) and a separate barometric pressure sensor; on those, P0109 can set when the two readings disagree by more than allowed. The sources differ on symptoms and causes: OBD-Codes.com describes noticeable drivability problems and black smoke and lists the barometric sensor and PCM as causes, while RepairPal says many cars show nothing but the check engine light and lists intake vacuum leaks. Related MAP sensor codes are P0105 (circuit malfunction), P0106 (range/performance), P0107 (low) and P0108 (high).

Severity: can I keep driving?

Drive with caution, fix soon

Get it checked soon. RepairPal rates P0109 Urgent, and OBD-Codes.com says it should be addressed urgently because the conditions behind it are likely to cause very poor fuel economy and drivability problems. RepairPal adds that in many cases there are no abnormal symptoms beyond the check engine light. If the engine hesitates badly, blows black smoke or runs poorly, avoid long or highway drives until it's fixed, and don't ignore a flashing check engine light.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Bad MAP sensor (OBD-Codes.com, RepairPal)
  2. Bad barometric pressure sensor, on vehicles that use a separate one (OBD-Codes.com, RepairPal)
  3. Open, shorted, loose or damaged MAP or barometric sensor wiring (OBD-Codes.com, RepairPal)
  4. Corroded connector at the MAP or barometric sensor (OBD-Codes.com, RepairPal)
  5. Intake manifold vacuum leaks, or a split seal where the sensor plugs into the manifold (RepairPal)
  6. Bad PCM or a PCM programming error (OBD-Codes.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Check for technical service bulletins (TSBs) for your vehicle first, since OBD-Codes.com notes this may be a known issue with a known fix.
  2. Read all stored codes and save the freeze frame data, which helps when the fault is intermittent. Diagnose any misfire codes first, since OBD-Codes.com says a poorly running engine won't make enough vacuum for the MAP sensor.
  3. Inspect the MAP sensor wiring, connector and vacuum hose, and the sensor seal if it plugs straight into the manifold. Fix any corrosion or damaged wiring before going further.
  4. Check engine vacuum with a vacuum gauge against your vehicle's spec. OBD-Codes.com says a clogged catalytic converter, restricted muffler or low fuel pressure can also cause low vacuum.
  5. With the key on and engine off, check the sensor connector for a steady 5-volt reference and a good ground. Then do a vacuum pump test while watching the MAP reading on a scan tool and wiggling the harness: RepairPal says the voltage should drop steadily from about 5 volts to under 1 volt as you apply 18 to 20 inches of vacuum. A reading that jumps or drops out while you wiggle the wiring points to the harness or connector.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • The check engine light is flashing or the engine misfires
  • You see black smoke or the engine hesitates badly
  • The code keeps returning after the sensor, wiring and vacuum checks pass
  • You suspect an EGR valve or idle air control problem, which RepairPal lists as common misdiagnoses
  • Testing needs a service manual, wiring diagram or PCM connector access you don't have (OBD-Codes.com advises disconnecting related controllers before ohmmeter tests to avoid damaging them)

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0109?

Usually for a short time, but don't put it off. Both sources treat it as urgent. If the car runs normally, drive gently and get it checked soon; if it hesitates, smokes or the check engine light flashes, avoid driving it.

Why does P0109 come and go?

It's the intermittent MAP code, so it often points to something that only fails some of the time, like a loose or corroded connector, chafed wiring or a split sensor seal. RepairPal suggests wiggling the harness during a vacuum pump test to catch it.

Should I just replace the MAP sensor?

Not before checking. RepairPal lists replacing the MAP sensor as a common misdiagnosis when the real cause is a vacuum leak, an EGR valve problem or a bad idle air control motor. Check the wiring, connector, hose and engine vacuum first.

How much does it cost to fix P0109?

Neither source gives a repair cost for P0109. Cleaning a corroded connector or fixing a vacuum hose is a much smaller job than a sensor or PCM, so find the cause before buying parts.

Sources

  1. OBD-Codes.com: P0109 MAP/Barometric Pressure Circuit Intermittent
  2. RepairPal: P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent (rated Urgent)

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.