P0171

What does this code mean?

P0171/P0172 refer to bank 1; P0174/P0175 to bank 2. Lean or rich describes the controller's mixture assessment, not a direct measurement of a failed part. Compare fuel trims at idle and under load, inspect air and exhaust leaks, and test fuel supply or sensor readings using vehicle-specific limits.

Sources and interpretation [1]

A code identifies a detected condition, not a part that must automatically be replaced.

Manufacturer wording

Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.

Original wording in English

A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.

Historical records · 7 · Historical vehicle association; OBD-II compatibility is not established by this record.

Before replacing a part

Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.

Scan worksheet →

Sources and interpretation

These explanations are editorial summaries of the linked manufacturer material. PDF page numbers count from the first file page. Original publications are in English; translations are reference aids. A cited edition is not a claim that it is the manufacturer's latest instruction.

1. 2024–2025 MY OBD System Operation Summary for Gasoline Engines ↗

   Ford Motor Company · PDF page(s) 21, 22 · 2024-04-16

Source check date · 2026-10-27

Can I keep driving?

A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.