CarSpecFix
OBD-II trouble code

P0171: System Too Lean, causes & can you keep driving?

Quick answer

What it means
System Too Lean[1]
Source wording: “P0171: System too Lean”
Wording from Mitsubishi service manual 13A-DTC P0171 (2022), web page
Can I keep driving?
It is important to note that an illuminated dashboard light, as described here, is intended to inform the driver of the need for service, NOT of the need to stop the vehicle. However, service should be sought as soon as possible.[2]
U.S. EPA Fact Sheet EPA 420-F-97-003 (May 1997), Frequently Asked Questions About On-Board Diagnostics, p.2 · applies to all OBD-II vehicles
Under certain conditions, the dashboard light will blink or flash. This indicates a rather severe level of engine misfire. When this occurs, the driver should reduce speed and seek service as soon as possible.[2]
U.S. EPA Fact Sheet EPA 420-F-97-003 (May 1997), Frequently Asked Questions About On-Board Diagnostics, p.2 · applies to all OBD-II vehicles
Toyota only If the malfunction indicator lamp comes on while driving First check the following: Is the fuel tank empty? If it is, fill the fuel tank immediately. Is the fuel tank cap loose? If it is, tighten it securely. The light will go off after several driving trips. If the light does not go off even after several trips, contact your Toyota dealer as soon as possible.[3]
Toyota only Malfunction indicator lamp ... Indicates a malfunction in: The electronic engine control system; The electronic throttle control system; or The electronic automatic transmission control system → Have the vehicle inspected by your Toyota dealer immediately.[3]
How urgent?
Not rated
Severity is rated only when a source states it.
Shop visit or check it yourself first?
Not yet verified — source pending
Last verified 2026-10-15Report a data error

Possible causes

Each cause comes from a manufacturer document and applies to the models listed. Your vehicle may differ.

  1. GM's service bulletin (GM PI1307 (2012-2014 Sonic), p.1) [4]
    Split air cleaner outlet duct after MAF letting unmetered air in
    Seen on: 2012-14 Chevrolet Sonic
  2. Ford's service bulletin (Ford PIP5549, p.1) [5]
    Vacuum leak in intake (foul-air/PCV tube) or purge valve
  3. Mazda's tech tip (Mazda M-Tip (P0171 Fuel Trim too Lean), p.1-2) [6]
    Air box/filter fitment, MAF, A/F sensor faults; fuel injectors
  4. VW's tech tip (VW Tech Tip 01-14-01TT, p.1) [7]
    Crankcase leak e.g. rear main seal / breather
    Seen on: Tiguan, Passat, CC, Jetta, Sportwagen, GTI, Eos; 2008-2017; 2.0L (CCTA, CBFA)
  5. Mitsubishi's service bulletin (Mitsubishi 13A-DTC P0171, Troubleshooting hints) [1]
    OEM list: A/F sensor, MAF, injector, fuel pressure, intake air leak at gaskets, ECT/IAT/baro/MAP sensors, exhaust leak, purge solenoid, contaminated fuel, harness, ECM
    Seen on: 2022 Mitsubishi models (service manual; specific model not named on the cited page)

Sources

  1. Mitsubishi service manual 13A-DTC P0171 (2022), web page, retrieved 2026-10-15
  2. U.S. EPA Fact Sheet EPA 420-F-97-003 (May 1997), Frequently Asked Questions About On-Board Diagnostics, p.2, retrieved 2026-10-15
  3. 2022 Toyota Camry Owner's Manual OM06244U, p.533, retrieved 2026-10-15
  4. GM PI1307 (2012-2014 Sonic), p.1, retrieved 2026-10-15
  5. Ford PIP5549, p.1, retrieved 2026-10-15
  6. Mazda M-Tip (P0171 Fuel Trim too Lean), p.1-2, retrieved 2026-10-15
  7. VW Tech Tip 01-14-01TT, p.1, retrieved 2026-10-15

General information from manufacturer documents, not professional mechanical advice. See Data sources.