Fuel and air

P2179 — System Too Lean Off Idle (Bank 2)

Severity: medium Drive with care, to a shop

What P2179 means

The engine control module detected that the air-fuel mixture on bank 2 of a V-type engine is too lean when driving off idle, under cruise or load. It reads mixture from the oxygen sensor and adds fuel through fuel trims. When trims hit their limit and the mixture is still lean, P2179 is stored and the check engine light comes on.

Symptoms

  • Check engine light on
  • Hesitation or roughness when accelerating
  • Rough running or misfire
  • Increased fuel consumption
  • Often appears with P0174 or other lean codes

Possible causes

  1. Vacuum or intake leak on the bank 2 side (hoses, manifold gaskets)
  2. Injector flow imbalance or clogged injectors
  3. Faulty bank 2 oxygen sensor (HO2S)
  4. Low fuel pressure (pump, filter, regulator)
  5. Exhaust leak ahead of the sensor skewing readings
  6. Damaged sensor wiring or short to positive
  7. Rarely, a faulty ECM

How to diagnose

  1. Scan for codes and freeze frame data, and note related codes such as P0174 or misfires
  2. Check short and long term fuel trims for bank 2 at idle and around 2500 rpm
  3. Inspect vacuum hoses, intake ducts and manifold gaskets, and smoke test for leaks
  4. Check MAF readings and look for leaks after the sensor
  5. Measure fuel pressure under load
  6. Test injectors: resistance, cylinder balance, and flow if needed
  7. Check the bank 2 oxygen sensor, its wiring and connector
  8. Inspect the exhaust for leaks upstream of the sensor

Common fixes

  • Repair intake leaks by replacing hoses or gaskets
  • Clean or replace injectors
  • Replace the fuel filter or pump if pressure is low
  • Replace the bank 2 oxygen sensor and repair wiring
  • Fix exhaust leaks
  • Clear codes and verify fuel trims afterward

Questions and answers

What does P2179 mean?

It means bank 2 is running too lean away from idle. The ECM adds fuel, but the correction isn't enough to reach a proper mixture.

Can I drive with P2179?

Briefly and gently until it is checked. Extended driving lean can cause misfires and overheat the catalytic converter.

What most often causes P2179?

Most often a vacuum leak on the bank 2 side, followed by low fuel pressure or clogged injectors. Start with fuel trims and a smoke test.

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.