Fuel and air

P2191 — System Too Lean at Idle (Bank 2)

Severity: medium Drive with care, to a shop

What P2191 means

The engine control unit reads the bank 2 oxygen sensor and sees too much air or too little fuel at idle. Fuel trims reach their limit and can no longer correct the mixture. The cause is usually an air leak or weak fuel delivery affecting that one bank.

Symptoms

  • Rough idle on a V-type engine
  • Check Engine light on
  • Misfires or unstable running
  • Possibly higher fuel consumption
  • Often appears with P0174 or other lean codes
  • Hesitation when pulling away

Possible causes

  1. Intake air leak on bank 2 (manifold gasket, intake boots)
  2. Cracked or disconnected vacuum hoses
  3. Faulty or dirty bank 2 oxygen sensor
  4. Low fuel pressure (pump, filter, regulator)
  5. Clogged or failing bank 2 injectors
  6. Exhaust leak ahead of the oxygen sensor
  7. Dirty mass airflow sensor

How to diagnose

  1. Read all codes and freeze-frame data, and compare with P0174/P0171
  2. Check short- and long-term fuel trims on both banks at idle and at 2500 rpm
  3. Inspect vacuum hoses, intake boots and manifold gaskets, and smoke test for leaks
  4. Check the exhaust for leaks upstream of the oxygen sensor
  5. Measure fuel pressure and compare it with specification
  6. Test injector circuits and cylinder balance on bank 2
  7. Evaluate the oxygen sensor signal and the MAF sensor condition

Common fixes

  • Replace the intake manifold gasket, boots or vacuum hoses
  • Repair the exhaust leak
  • Clean or replace the injectors
  • Replace the fuel filter or pump if pressure is low
  • Replace a faulty oxygen sensor or MAF sensor

Questions and answers

What does P2191 mean?

It means the mixture on bank 2 is too lean at idle. The engine is getting too much air or too little fuel, and the computer cannot fully correct it.

Can I drive with P2191?

Briefly and carefully until it is repaired. A lean mixture can cause overheating and misfires, and over time it can damage the catalytic converter.

Where should I start diagnosing P2191?

Start by looking for an air leak: check hoses and the intake manifold gasket on bank 2, then check fuel pressure and fuel trims.

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.