Fuel & air metering · Powertrain · generic (SAE-defined)
P2279: Intake Air System Leak
P2279 means the engine computer detected air entering the intake that is not being measured, pointing to a leak somewhere between the airflow sensor and the engine.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P2279 sets
The powertrain control module (PCM) compares measured airflow from the mass air flow (MAF) or manifold pressure sensor with expected airflow and fuel correction. When the comparison and fuel trims indicate more air is reaching the engine than was measured, the PCM concludes there is an intake leak. Detection strategies vary by manufacturer.
Common causes of P2279
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Cracked or loose intake air duct or boot
- Leaking intake manifold gasket
- Cracked vacuum hose or fitting
- Faulty positive crankcase ventilation (PCV) valve or hose
- Leaking throttle body gasket
- Brake booster or booster hose leak
- Leaking idle air control or purge connection
P2279 symptoms
- Check engine light on
- Rough or high idle
- Hissing noise from the engine bay
- Hesitation or stalling
- Lean codes such as P0171 or P0174
How P2279 is diagnosed
- Scan for all codes and freeze frame; note any lean or MAF codes.
- Visually inspect intake ducts, clamps, and vacuum hoses.
- Check fuel trims at idle and higher rpm; trims that improve with rpm suggest a vacuum leak.
- Perform a smoke test of the intake system.
- Inspect the PCV system and brake booster hose.
- Verify MAF readings once leaks are repaired.
Typical fixes for P2279
- Replace cracked intake ducts or boots
- Replace leaking vacuum hoses
- Replace the intake manifold or throttle body gasket
- Replace the PCV valve or hoses
- Repair brake booster leaks
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Commonly reported on some GM engines, where intake and PCV-related leaks are frequent suspects; check factory service information.
Related codes & warning lights
P2279 FAQ
What does code P2279 mean?
P2279 means the engine computer detected air entering the intake that is not being measured, pointing to a leak somewhere between the airflow sensor and the engine. The standard definition is "Intake Air System Leak."
Can I drive with a P2279 code?
Usually yes for short trips, though the idle may be rough. Repair it within days, because a lean mixture can cause stalling, misfires, and added engine stress.
How do shops find the leak for P2279?
A smoke test is the usual method: low-pressure smoke is fed into the intake and escapes wherever there is a leak.
Can a loose oil filler cap cause P2279?
On engines where the crankcase is connected to the intake through the PCV system, a loose or missing oil cap can let unmetered air in.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.