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Home / Codes / P0173
DTC code page

P0173: Fuel Trim Malfunction (Bank 2)

Quick answer: The ECU sees a fuel-trim control problem on Bank 2 rather than a clean lean-only or rich-only pattern.

Drivers also search this fault as fuel trim malfunction bank 2, bank 2 fuel trim fault, fuel correction malfunction bank 2.

Severity: medium Family: powertrain Related paths: 11
Meaning

What P0173 usually means

P0173 is the Bank 2 partner to P0170. It means the ECU no longer trusts how Bank 2 fuel correction is behaving. That can happen when a bank-specific air leak, injector problem, oxygen-sensor issue, or broader airflow error makes trim behavior unstable or implausible. It is best approached by comparing both banks instead of reading the code title as proof that the engine is simply rich or simply lean.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Compare Bank 1 and Bank 2 trim behavior before replacing anything.
  • Look for bank-specific clues such as a leak, exhaust issue, or injector evidence affecting only Bank 2.
  • Check for companion airflow or O2 codes that explain why trim plausibility failed.
Driving risk

Can you keep driving?

P0173 is often driveable short-term, but unstable trim control can worsen idle quality, fuel economy, and emissions if the root cause keeps drifting.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • Bank 2 air leak or manifold problem distorting trim control
  • Bank 2 front O2 sensor feedback issue
  • Dirty or biased MAF sensor affecting both banks but surfacing on Bank 2
  • Fuel pressure or injector-balance issue changing Bank 2 correction behavior
  • Adaptation values learned too far from normal because an older fault was never corrected cleanly

Cause phrases often tied to this code: bank 2 vacuum leak, bank 2 O2 sensor issue, dirty MAF, fuel pressure problem, injector imbalance.

Diagnostic order

Suggested workflow

  1. Compare both banks at idle and cruise to see whether Bank 2 is uniquely unstable.
  2. Inspect Bank 2 for intake leaks, exhaust leaks, or injector clues.
  3. Review MAF plausibility and front O2 sensor behavior.
  4. Confirm fuel pressure and delivery before blaming the sensor side alone.
  5. After repair, verify both banks relearn normally and the Bank 2 fault does not return.
Avoid guesswork

Common mistakes

  • Replacing a Bank 2 oxygen sensor before comparing actual trim data between banks.
  • Assuming P0173 always means the same fix as P0170 without checking which bank is actually unstable.
  • Ignoring the possibility that an old vacuum or fuel issue left trim adaptation far from normal.
Repair path

Practical fix guidance

  • Fix the bank-specific air, fuel, or sensor issue that best fits the comparison data.
  • If both banks are unstable, shift the diagnosis toward shared airflow, fuel pressure, or global sensor inputs.
  • Retest through idle, light cruise, and warm restart conditions after clearing codes.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0173

Useful when the driver knows the wording but not the exact DTC yet.

  • fuel trim malfunction bank 2
  • bank 2 fuel trim fault
  • fuel correction malfunction bank 2
Related search intent

Queries this page can answer naturally

  • P0173 code meaning
  • what does P0173 mean
  • fuel trim malfunction bank 2 symptoms
  • P0173 vs P0174
FAQ

Quick questions about P0173

Is P0173 the same as P0170?

They describe the same kind of trim-control problem, but on opposite banks of the engine.

Can P0173 be caused by a vacuum leak?

Yes. A bank-specific air leak can make Bank 2 trim behavior unstable enough to trigger P0173.

Do I diagnose P0173 like a lean code or a rich code?

Start with trim data. P0173 is a trim-control code, so the real pattern may be lean, rich, unstable, or inconsistent.