Fuel trim and air/fuel mixture
P0171
System Too Lean (Bank 1)
What does P0171 mean?
P0171 means the engine computer has been adding extra fuel for too long to correct a mixture it sees as too lean on bank 1. Lean means too much air relative to fuel. The code is set when the correction the computer is applying runs past the limit it is allowed to compensate within.
Can I keep driving with P0171?
Moderate urgency
Drivable in the short term, but a sustained lean condition runs the engine hotter than intended and is worth resolving before it causes misfires or converter damage.
Symptoms of P0171
Rough or hunting idle
Hesitation or a flat spot on acceleration
Check engine light with otherwise normal driving
Sometimes a whistling or hissing noise from a vacuum leak
Common causes of P0171
A vacuum leak — cracked hose, failed intake gasket or a leaking PCV line
A dirty or failing mass airflow sensor reading low
Weak fuel delivery: failing pump, clogged filter or dirty injectors
An exhaust leak ahead of the upstream oxygen sensor
These are ordered roughly by how often they turn out to be the cause — but the code names a system, not a part. Confirming which one is yours takes data from the running engine.
What does it cost to fix P0171?
$100 – $900
Typical US independent-shop range, parts and labour included. It is wide on purpose: the cheap end is usually a sensor, a hose or a cap, and the expensive end is the major component the code was reporting on. Which one you need is a diagnosis, not a guess — and dealer rates run higher than these figures.
What does P0171 mean for your car?
This page explains what P0171 means in general. It cannot tell you which of those causes is yours, because that answer is in your car's own data. Kaiju Mechanic reads the codes your car is actually storing, plus live sensor data through any standard ELM327 adapter, and interprets it against your exact year, make, model and mileage. You can also just ask it about P0171 in chat — no adapter needed for that.
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