Code
P0109
GWM
P — Powertrain
- Intake Manifold Absolute Pressure / Intake Manifold Pressure Sensor Malfunction | Intake Air Temperature Sensor Circuit Malfunction
Views:
UK: 17
EN: 28
RU: 24
AI status
Completed
Completed
100%
Causes
- Failed MAP sensor
- Failed IAT sensor (NTC thermistor)
- Damaged, corroded or disconnected wiring/connectors to MAP or IAT
- Short to battery or ground in signal or reference circuits
- Vacuum leaks or blocked MAP sensor port/vent
- Intake air passages contaminated with oil/debris or water intrusion
Symptoms
- Check Engine Lamp (CEL) illuminated
- Poor idle quality, surging or stalling
- Reduced engine power or hesitation under load
- Hard starting or poor cold-start behavior
- Elevated fuel consumption or black smoke from exhaust
- Incorrect barometric correction (affects alt compensation)
What to check
- Read freeze-frame and live data with a scan tool: MAP pressure (kPa/inHg) and IAT temperature (°C/°F) values and response to throttle/vacuum changes
- Visual inspection of MAP and IAT connectors, wiring, and intake vacuum hoses for damage or contamination
- Backprobe sensor connector to verify 5V reference (or manufacturer-specified reference), sensor ground and signal voltage
- Check for stored related codes (e.g., MAP or IAT circuit codes) and pending intermittent codes
- Wiggle test wiring while viewing live data to spot intermittent faults
- Inspect MAP sensor port/vent for blockage; check for intake vacuum leaks
Signal parameters
- MAP sensor signal: typically ~0.5 V (high vacuum) to ~4.0–4.5 V (high pressure/boost) depending on engine/sensor — should change smoothly with throttle/vacuum
- MAP sensor reference: stable 5 V (or manufacturer spec) supply present at sensor connector with ignition ON
- MAP sensor ground: good continuity to chassis/ECM ground; near 0 Ω path
- IAT sensor: NTC thermistor — resistance decreases as temperature rises; sensor voltage typically in the 0.5–4.5 V range depending on ambient temp and vehicle circuit
- IAT expected resistance: varies by sensor type; many common IATs are ~2–20 kΩ at typical ambient temperatures — verify against manufacturer spec
- No rapid voltage spikes, random opens (OL) or short-to-voltage/ground on either signal line
Diagnostic algorithm
- Confirm code and record freeze-frame/live MAP and IAT readings with a scan tool. Note engine load, RPM, intake vacuum/pressure and ambient conditions.
- Perform a visual inspection of sensors, connectors and wiring; repair any obvious damage, corrosion or loose pins.
- With ignition ON (engine off), backprobe connector: verify stable reference voltage (5 V), sensor ground continuity, and signal voltage present. If reference or ground missing, trace wiring to ECU.
- For MAP: observe signal voltage while applying vacuum (handheld pump) or changing throttle — voltage should change smoothly with pressure. If signal does not respond correctly, suspect sensor or wiring.
- For IAT: measure resistance of sensor at known ambient temperature and compare to expected values (service spec). Alternatively monitor IAT voltage/temperature with scan tool and compare to ambient temperature. Replace if out of range or open/shorted.
- Check for intake vacuum leaks, blocked MAP vents or clogged sensor ports; clean or replace as needed.
- Check continuity and insulation of wiring to ECU; repair any short to power or ground. Use wiring diagrams to identify circuit colors and pin locations.
- If wiring and connectors are good but sensor readings remain incorrect, replace the affected sensor(s) (MAP and/or IAT).
- Clear codes, perform test drive and re-scan to confirm the fault does not return. If code returns after sensor/wiring replacement, consider ECU input circuit diagnosis or ECU replacement as last resort.
Likely causes
- Corroded or loose connector at MAP or IAT
- Broken wire or intermittent contact in harness (flex points, near firewall)
- MAP sensor internal failure (stuck/stiff diaphragms or electronic fault)
- IAT thermistor open/shorted or contaminated
- Blocked or leaking MAP reference/vacuum hose
- Water ingress in intake or sensor connector after washing/driving in deep water
Fault status
Status
P0109 — Intake Manifold Pressure (MAP) and/or Intake Air Temperature (IAT) sensor circuit malfunction. Verify MAP and IAT sensor signals, reference voltage, ground, connectors, and wiring. Inspect intake for leaks or contamination. Replace faulty sensor or repair wiring as required.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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