Loose, corroded, or damaged electrical connector at the MAP or BARO sensor; Chafed or broken wire in the sensor signal or ground circuit; Failing MAP or BARO sensor with an intermittent internal fault; Vacuum hose connected to the MAP sensor that is cracked, soft, or loose; Poor ground connection for the sensor circuit at the engine block or chassis; Intake manifold vacuum leak causing erratic pressure readings; Faulty engine computer, though this is rare

DTC codes / P01xx · Fuel and air metering / P0109

P0109MAP/Barometric Pressure Circuit Intermittent

Q: What does code P0109 mean?

MAP/Barometric Pressure Circuit Intermittent. P0109 means the engine computer has detected an intermittent fault in the manifold absolute pressure (MAP) sensor circuit or, on some vehicles, the barometric pressure (BARO) circuit. The signal from the sensor momentarily drops out or jumps erratically, so the computer cannot trust the pressure reading for fuel delivery and ignition timing calculations.

P0109 means the engine computer has detected an intermittent fault in the manifold absolute pressure (MAP) sensor circuit or, on some vehicles, the barometric pressure (BARO) circuit. The signal from the sensor momentarily drops out or jumps erratically, so the computer cannot trust the pressure reading for fuel delivery and ignition timing calculations.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Engine may stumble or hesitate under acceleration when the fault occurs
Rough idle or fluctuating idle speed
Poor fuel economy or rich/lean running conditions
Occasional hard starting or stalling when coming to a stop
A slight surge or lack of power during steady cruising

Common causes, most likely first

Loose, corroded, or damaged electrical connector at the MAP or BARO sensor
Chafed or broken wire in the sensor signal or ground circuit
Failing MAP or BARO sensor with an intermittent internal fault
Vacuum hose connected to the MAP sensor that is cracked, soft, or loose
Poor ground connection for the sensor circuit at the engine block or chassis
Intake manifold vacuum leak causing erratic pressure readings
Faulty engine computer, though this is rare

How to diagnose and fix it

Inspect the MAP or BARO sensor connector and wiring for looseness, corrosion, or damage; clean and secure as needed
Check all vacuum hoses connected to the MAP sensor for cracks, softness, or disconnection and replace any faulty hose
Use a scan tool to view live MAP or BARO data while wiggling the harness and connector to spot intermittent dropouts
Measure the sensor reference voltage and ground with a multimeter, then check the signal voltage with a vacuum pump applied to the sensor
Perform a voltage drop test on the ground circuit to confirm a solid ground connection
Replace the MAP or BARO sensor if testing shows an internal intermittent fault
Clear the code and verify the repair by test-driving under conditions that previously set the code

Intermittent faults hide in connectors and grounds

A loose or corroded connector pin is the most common cause of an intermittent MAP code, yet many people replace the sensor first and the code returns.
On some vehicles the barometric pressure sensor is integrated into the mass airflow sensor or the engine computer, so the fault may not be at a separate MAP sensor.
A vacuum leak can cause the MAP signal to fluctuate enough to set an intermittent code without any hard fault, so always check intake hoses and gaskets.
The code can set during a brief glitch that lasts only milliseconds, so the sensor may test perfectly good when the engine is idling in the shop.
A poor engine ground can affect multiple sensors and cause a P0109 along with other unrelated codes, so inspect ground straps and battery terminals.

Can I keep driving with P0109?

You can usually drive the vehicle with a P0109 code, but avoid aggressive acceleration or heavy loads until the fault is repaired because the engine may hesitate or stall unexpectedly. If the engine runs poorly or stalls frequently, have it diagnosed promptly to prevent unsafe driving conditions.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.