P0171 Code: System Too Lean (Bank 1)
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Was bedeutet das?
Code P0171 indicates the engine control module has detected that the fuel system on Bank 1 is running too lean — there is too much air or too little fuel in the air-fuel mixture. The long-term fuel trim has exceeded its adjustment range.
Diagnostic system: Fuel trim and air metering
On a Subaru Outback, the P0171 code should be diagnosed as part of the fuel trim and air metering group. Related codes and live data from this same system can change the repair priority, so avoid replacing parts from the code name alone.
Most Common Causes for Subaru Outback
- Vakuumleck im Ansaugsystem
- Verschmutzter oder verunreinigter MAF-Sensor
- Schwache oder defekte Kraftstoffpumpe
- Verstopfter Kraftstofffilter
- Defekter Kraftstoffdruckregler
- Verstopfte oder defekte Einspritzdüse
- Undichte Ansaugkrümmerdichtung
- Abgasleck vor der Lambdasonde
- Defekte Lambdasonde (O2-Sensor)
Zu beachtende Symptome
- Motorkontrollleuchte leuchtet
- Unruhiger oder instabiler Leerlauf
- Zögern oder Stottern beim Beschleunigen
- Schlechte Beschleunigung oder träge Reaktion
- Motor geht unerwartet aus
- Erhöhter Kraftstoffverbrauch
- Fehlzündungen oder Ruckeln des Motors
- Schwierigkeiten beim Starten des Motors
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- Read short-term and long-term fuel trims at idle and cruise.
- Inspect intake boots, vacuum hoses, PCV plumbing, and MAF sensor contamination.
- Check fuel pressure if trims suggest a lean condition under load.
- Check for blown fuses, weak battery voltage, and damaged connectors before buying major parts.
Wie man diagnostiziert
CodePage.commonMistakes
Replacing oxygen sensors because they report lean/rich exhaust when the real cause is air, fuel pressure, or MAF data. Always confirm the fault with freeze-frame data, live data, visual inspection, and circuit checks before spending money on parts.
CodePage.faq
Can I drive with the P0171 code?
If the check engine light is solid, you can usually drive to a safe location or mechanic. If the light is flashing, pull over immediately to prevent catastrophic engine or catalytic converter damage.
Will the P0171 code clear itself?
Once the underlying problem is fixed, the engine computer will run its self-checks. If it passes over several drive cycles, the light will turn off automatically. You can also clear it immediately using an OBD2 scanner.
Will this code fail an emissions test?
Yes. If the Check Engine Light is on due to the P0171 code, your Subaru will automatically fail an OBD2 plug-in emissions or smog test.
What should I check first for P0171?
Read short-term and long-term fuel trims at idle and cruise. Inspect intake boots, vacuum hoses, PCV plumbing, and MAF sensor contamination. Check fuel pressure if trims suggest a lean condition under load.
Join the Discussion
Reparaturkosten
Vacuum leak repair, MAF cleaning, or PCV hose repair
Major component replacement after live data and circuit tests confirm failure
Beinhaltet Teile und Arbeit. Kann je nach Standort variieren.
Vacuum leaks and cleaning are cheap; fuel pump, injector, or MAF replacement costs more and should be verified.
DIY-Schwierigkeitsgrad
Can usually be performed at home with basic hand tools.