Fuel and air

P2279 — Intake Air System Leak

Severity: medium Drive with care, to a shop

What P2279 means

The ECM compares the airflow the MAF sensor reports with what fuel trims and manifold pressure indicate, and it notices when extra air is getting in. Normally all intake air passes through the filter and MAF, and the tract is sealed all the way to the cylinders. A leak leans out the mixture and throws off fueling calculations.

Symptoms

  • Whistling or hissing from the engine bay
  • Rough or surging idle
  • Lean codes P0171 and P0174
  • Check Engine light on
  • Loss of power, especially on turbocharged engines
  • Hard brake pedal if the booster hose is leaking

Possible causes

  1. Cracked intake boot between the MAF and throttle body
  2. Loose or popped-off intercooler hose
  3. Leaking intake manifold gasket
  4. PCV hose disconnected or cracked
  5. Damaged brake booster vacuum hose
  6. Mechanical engine fault

How to diagnose

  1. Read all codes and freeze frame data, and note the fuel trims (STFT/LTFT).
  2. Inspect the intake tract from the MAF to the manifold: boots, clamps, hoses and connectors.
  3. Check intercooler hoses and clamps for cracks and oil residue.
  4. Inspect vacuum lines, the PCV hose and the brake booster hose.
  5. Smoke test the intake with the engine running to pinpoint the leak.
  6. Compare trims at idle and at higher RPM: lean at idle that improves with revs points to a leak.
  7. Check the intake manifold gasket and bolt torque.
  8. Make sure the MAF sensor is clean and working properly.

Common fixes

  • Replace the cracked intake boot or duct
  • Tighten or replace intercooler hoses and clamps
  • Replace the intake manifold gasket
  • Replace vacuum hoses and the PCV hose
  • Clear codes and reset adaptations after the repair

Questions and answers

What does P2279 mean?

It means air is entering the engine without passing through the MAF sensor. That leans out the mixture, so P0171 and P0174 often appear alongside it.

How do I find an intake air leak myself?

Look over the hoses and clamps and listen for hissing at idle. A smoke test is the most reliable way to show exactly where the leak is.

Can I drive with P2279?

Briefly, yes, but don't put the repair off. A lean mixture can overheat the engine and damage the catalytic converter.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.