P0173 — Fuel Trim Bank 2

P0173: Fuel Trim Bank 2 — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

Fuel Trim Bank 2. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • Check-engine lamp, possible hesitation, irregular idle or increased fuel consumption.
  • Bank 2 fuel trims may move outside the control range; the code alone does not prove a lean or rich condition.

Possible causes

  • Unmetered intake air or an exhaust leak close to mixture-monitoring sensors.
  • Biased MAF/oxygen sensing, incorrect fuel supply or injector imbalance affecting bank 2.

What to check

  • Confirm P0173 and record freeze-frame and related rich/lean or misfire codes.
  • Compare bank 2 short- and long-term trims with bank 1 at idle and higher load, where supported.
  • Check for intake vacuum leaks, exhaust leaks and MAF signal plausibility.
  • Measure fuel-system operation only at manufacturer-specified test points; inspect injectors if evidence points to imbalance.
  • Repair the demonstrated cause and validate fuel-trim changes, avoiding arbitrary reset-only fixes.

Also written as: P0173-00, P017300, PO173 (some scan tools add the fault-type byte, e.g. -00).