P0174 — System Too Lean Bank 2

Fuel trims indicate a lean tendency on bank 2: the controller adds fuel to compensate. Bank 2 is the cylinder group that does not contain cylinder 1. The code alone does not prove oxygen-sensor failure; identify the real or reported mixture problem.

Affected system: Powertrain

Symptoms

• Uneven idle, hesitation or reduced power.
• Engine warning light; misfires can occur when the mixture becomes excessively lean.

Possible causes

• Intake/PCV leak, insufficient fuel supply or restricted injector.
• Biased MAF or an exhaust leak ahead of bank 2’s sensor causing a false lean report.

What to check

• Locate bank 2 and save RPM, load and temperature; address related sensor or misfire codes first.
• Compare both banks’ STFT/LTFT at idle and moderate load with the engine warm and fuel control active.
• If the deviation is greatest at idle, investigate unmetered air on bank 2; also check the exhaust before its sensor.
• Measure fuel pressure/delivery to OEM specifications and evaluate MAF/oxygen-sensor response before replacing the pump or sensors.
• After repair, clear codes and recheck both banks’ fuel trims under the original recorded conditions, following the manufacturer’s procedure.

Also written as: P0174-00, P017400, PO174 (some scan tools add the fault-type byte, e.g. -00).