P0171 OBD-II code — what it means and what to check

ℹ Guidance only — not a substitute for inspection

Enter the trouble codes from your scanner to see what each one means, how urgent it is, and which checks to do first.

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Your trouble codes

Enter the codes exactly as your scanner shows them. Separate several codes with spaces or commas.

A letter followed by four characters, for example P0301. Up to ten codes at a time.
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Your codes, interpreted

What this means
⚠ Book a service. The codes you entered describe faults that get worse, or more expensive, if left.
What to doBook a workshop inspection. Normal driving is usual with these faults, but they should not be left indefinitely.

Your codes

  1. P0171 — Fuel and air metering (service soon). Bank 1 is running lean: the engine computer is adding fuel to compensate and has run out of adjustment. Extra air is getting in, or not enough fuel is being delivered.

Checks to do first, in order

  1. Inspect intake hoses, the PCV system and the intake manifold gasket for vacuum leaks — this is the most common cause by a wide margin.
  2. Check the mass air flow sensor for contamination.
  3. Have fuel pressure and the fuel filter checked if no leak is found.
  4. Look for exhaust leaks ahead of the upstream oxygen sensor.

Codes this tool cannot interpret

How this result was reached
  • Interpretations cover standardised codes only, and describe what a code means rather than what is wrong with your specific vehicle.
  • A stored code identifies the circuit or system reporting a fault. It does not identify the failed part — a sensor commonly reports a problem it did not cause.
  • Reviewed by Project Owner on 2026-08-26.
  • This tool covers a reviewed subset of standardised codes. A code it does not recognise is reported as undocumented rather than guessed at.