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DTC codes / U35xx · Network communication / U3559

U3559Air Inlet Pressure Sensor Circuit

U3559 indicates that the powertrain control module (PCM) has detected an abnormal signal from the air inlet pressure sensor circuit, which measures the pressure of air entering the engine. The PCM sets this code when the sensor's voltage or signal falls outside the expected range for the current operating conditions, often due to a wiring fault, sensor failure, or intake leak.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light (malfunction indicator lamp) on the dashboard.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.
  • Rough idle or stumbling, particularly when the engine is cold.
  • Reduced engine performance or hesitation during acceleration.
  • Poor fuel economy due to incorrect air pressure readings affecting fuel delivery.
  • In some cases, the engine may enter limp mode or exhibit limited power.

Common causes, most likely first

  1. Faulty air inlet pressure sensor (also known as a boost pressure sensor or intake air pressure sensor).
  2. Damaged or corroded wiring or connector at the sensor or PCM.
  3. Intake air leak between the air filter and throttle body, such as a cracked intake hose or loose clamp.
  4. Clogged or restricted air filter or intake duct.
  5. Failed sensor reference voltage or ground circuit.
  6. PCM software issue or internal fault (rare).

How to diagnose and fix it

  1. Inspect the air intake system for leaks, cracks, or loose connections, and repair as needed.
  2. Check the air filter and intake duct for restrictions and replace if clogged.
  3. Disconnect the sensor connector and inspect for corrosion, bent pins, or damaged wires; clean or repair as necessary.
  4. Measure the sensor's reference voltage (typically 5V) and ground circuit with a multimeter to verify proper power and ground.
  5. Test the sensor's signal output with a scan tool or multimeter while varying engine speed; compare to manufacturer specifications and replace if out of range.
  6. Clear the diagnostic trouble codes and perform a road test to verify the repair; if the code returns, further diagnose the PCM and wiring harness.

Before you replace the air inlet pressure sensor

  • A loose or cracked intake hose after the mass airflow sensor can cause this code without any sensor fault, so always perform a visual inspection and smoke test first.
  • The air inlet pressure sensor is often confused with the mass airflow sensor (MAF) or manifold absolute pressure (MAP) sensor; verify which sensor your engine uses and its location before testing.
  • Intermittent wiring faults from chafed harnesses near hot or moving components are a common cause that may not appear during a simple resistance check.
  • A dirty or contaminated sensor element can produce skewed readings without setting a hard fault; cleaning with approved electronics cleaner may resolve the issue.
  • This code can be set by a PCM calibration issue; check for technical service bulletins (TSBs) or software updates before replacing hardware.

Can I keep driving with U3559?

You can usually continue driving with this code, but avoid aggressive acceleration or heavy loads until it is repaired, as incorrect air pressure readings can affect fuel mixture and engine performance. If the engine runs poorly or enters limp mode, seek service promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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