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Home / DTC / P0109 — Manifold Absolute Pressure/Barometric Pressure Sensor Circuit Intermittent

P0109 — Manifold Absolute Pressure/Barometric Pressure Sensor Circuit Intermittent

Detailed page for trouble code P0109.

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P0109

Generic P — Powertrain

Manifold Absolute Pressure/Barometric Pressure Sensor Circuit Intermittent

Brand: Generic
Type: P — Powertrain
Views: UK: 17 EN: 41 RU: 29
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Page language: EN

Causes

  • Intermittent/open/short in MAP sensor wiring or connector
  • Corroded or loose sensor connector pins
  • Failing MAP/BARO sensor (internal intermittent)
  • Intermittent 5V reference or ground to the sensor
  • Intermittent ECM input pin or poor ECM connector contact
  • Intake leaks or vacuum issues causing erratic readings

Symptoms

  • Intermittent Check Engine Light (MIL) or stored intermittent DTC
  • Irregular idle, surging, stalling or hesitation
  • Reduced engine performance or throttle response
  • Poor fuel economy or increased emissions
  • Hard starting in some conditions

What to check

  • Read freeze frame and full DTC history with a scan tool; note when the fault set
  • Monitor MAP/BARO live data while starting and under different loads (idle, accelerate)
  • Perform visual inspection of MAP sensor, connector, and wiring for damage, corrosion, or oil contamination
  • Back-probe connector to confirm steady 5V reference and good ground
  • Wiggle test wiring and connectors while watching live data/scan tool for intermittent changes
  • Check continuity and resistance of sensor power/ground/signal wires to ECM (with ignition off)

Signal parameters

  • Reference voltage: typically ~5.0 V (ECM supplied) — should be stable
  • Sensor ground: ~0 V, low resistance to chassis/ECM ground
  • Sensor signal: nominally 0.5–4.5 V (approximate) depending on absolute pressure — at ambient/barometric pressure the signal is near the high end (~3.5–4.8 V depending on sensor), at high vacuum the voltage is lower (~0.5–2.5 V); values vary by sensor and vehicle
  • Signal should change smoothly with engine vacuum/load; spikes, dropouts, or rapid jumps indicate intermittency

Diagnostic algorithm

  1. Retrieve and record DTC freeze frame and stored events. Note conditions when P0109 set (rpm, load, temperature).
  2. With a scan tool, monitor MAP/BARO live data while key on/engine off (baro) and during cranking/running. Confirm whether readings are stable or drop out intermittently.
  3. Visually inspect connector and wiring at the MAP sensor. Disconnect, inspect pins for corrosion, bent pins, or contamination. Re-seat connector securely.
  4. Back-probe sensor connector: verify stable 5V reference and sensor ground at key on and while engine runs. If reference or ground is intermittent, trace wiring to ECM and repair.
  5. Perform a wiggle test: with scanner monitoring MAP signal, gently move wiring harness, connectors, and sensor while observing for intermittent signal changes or DTC set. Pay attention to factory harness routing and common chafe points.
  6. Check continuity and resistance of signal, power, and ground wires from sensor to ECM connector with ignition off. Repair any opens/shorts; ensure good pin-to-pin continuity.
  7. Measure MAP sensor output voltage while applying known vacuum levels (hand vacuum pump) or comparing to barometric reading. Replace sensor if output is erratic or jumps.
  8. If wiring and sensor check good, inspect ECM connector and pins for corrosion or loose terminals. Wiggle-test at the ECM end if accessible.
  9. If intermittent persists and wiring/sensor repaired, consider replacing the MAP/BARO sensor. If problems remain after sensor and harness repairs, suspect ECM input intermittency and consult manufacturer resources before replacing ECM.
  10. After repair, clear codes and road-test under the original freeze-frame conditions to confirm the fault does not return.

Likely causes

  • Damaged or chafed wire between sensor and ECM
  • Corroded/loose connector at the MAP sensor
  • Failing MAP/BARO sensor
  • Poor or intermittent sensor ground
  • Intermittent 5V reference from ECM

Fault status

⚠️ Status
Intermittent MAP/BARO sensor circuit detected by ECM. Signal was unstable or lost intermittently. May cause erratic engine operation; further diagnosis of wiring, connector, sensor, and ECM input required.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours (may be longer for intermittent wiring faults)

Similar codes

P0106 P0107 P0108 P0104 P0193
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