P0173 Fuel Trim Malfunction Bank 2

P0173 indicates a fuel trim malfunction on bank 2. The controller cannot keep bank 2 fuel correction within expected limits.

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 parts by bank number alone; compare bank 1 and bank 2 data to isolate the cause.

Symptoms of P0173

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0173

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare bank 2 fuel trims with bank 1, oxygen sensor activity, airflow data, fuel pressure, and freeze-frame load conditions.
Inspect bank-specific intake leaks, exhaust leaks, injector issues, vacuum leaks, PCV routing, and sensor or wiring faults.
Determine whether the trim problem is rich, lean, idle-only, load-dependent, or tied to misfire or catalyst codes.

Related OBD-II codes

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