Fuel and air

P0174 — System Too Lean (Bank 2)

Severity: medium Drive with care, to a shop

What P0174 means

The engine computer watches the air-fuel mixture through the oxygen sensors and adds or removes fuel with fuel trims. P0174 sets when Bank 2 trims stay far on the positive side and the mixture is still too lean, meaning too much air or too little fuel. The usual culprits are unmetered air or weak fuel delivery.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Weak acceleration and low power
  • Worse fuel economy
  • Misfires or hesitation
  • Often appears together with P0171

Possible causes

  1. Vacuum leaks on Bank 2: intake manifold gaskets, hoses, PCV system
  2. Dirty or faulty mass airflow (MAF) sensor
  3. Low fuel pressure from a weak pump or clogged filter
  4. Clogged or failing Bank 2 fuel injectors
  5. Faulty upstream oxygen sensor on Bank 2
  6. Exhaust leak ahead of the oxygen sensor skewing readings

How to diagnose

  1. Scan for codes and freeze-frame data, and note whether P0171 is also stored
  2. Watch short- and long-term fuel trims at idle and around 2,500 rpm
  3. Inspect vacuum hoses, intake ducts and manifold gaskets, and smoke-test or spray-test for leaks
  4. Check MAF readings and sensor condition, and clean it with MAF-safe cleaner if dirty
  5. Measure fuel pressure and compare it to the factory spec
  6. Inspect the exhaust for leaks upstream of the oxygen sensor
  7. Check Bank 2 injector operation and cylinder balance
  8. Check the Bank 2 oxygen sensor signal with a scan tool or scope

Common fixes

  • Repair vacuum leaks: replace hoses, manifold gaskets or PCV parts
  • Clean or replace the MAF sensor
  • Replace the fuel filter or pump if pressure is low
  • Clean or replace Bank 2 injectors
  • Replace a faulty Bank 2 oxygen sensor
  • Repair exhaust leaks

P0174 on different brands

Ford · manuals
Ford lists P0174:00 in its 2024-2025 gasoline-engine OBD strategy as system too lean (Bank 2); it reports the condition the monitor detected, not a confirmed failed part.

Questions and answers

What does P0174 mean?

The computer found the Bank 2 mixture too lean and fuel trim could not correct it. Common causes are a vacuum leak, a MAF sensor problem or low fuel delivery.

Can I drive with P0174?

Briefly and gently, yes. If the engine misfires or the check engine light flashes, stop driving, because a lean mixture can overheat the engine and damage the catalytic converter.

Why do I get P0174 and P0171 together?

When both banks run lean, the cause is usually shared: a vacuum leak after the MAF sensor, a dirty MAF sensor or low fuel pressure.

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.