P0174 System Too Lean Bank 2

P0174 means the control module reports a lean condition on bank 2. It is similar to P0171, but the affected bank matters when checking vacuum leaks, exhaust leaks, injectors, and sensor data.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace both upstream sensors automatically; bank-to-bank trim comparison usually gives a better diagnostic direction.

Symptoms of P0174

Rough or lopey idle, sometimes stalling.
Hesitation or lack of power under acceleration.
Check-engine light with elevated long-term fuel trims.
Occasional light surging at steady cruise.

Common causes of P0174

Unmetered air — a vacuum leak, split intake boot, or PCV hose.
A dirty or failing mass-airflow (MAF) sensor.
Low fuel pressure or weak/clogged injectors.
An exhaust leak near the upstream oxygen sensor.

Useful checks before replacing parts

Compare bank 1 and bank 2 fuel trims to decide whether the problem is bank-specific or engine-wide.
Inspect intake manifold sealing, PCV plumbing, exhaust leaks, injector delivery, and bank 2 oxygen or air-fuel sensor data.
Use freeze-frame data to see whether the lean condition appeared at idle, cruise, acceleration, or high load.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.