P0171 on Acura
System Too Lean (Bank 1)
P0171 on Acura vehicles indicates system too lean (bank 1). Au7o has documented this code across 1 Acura model — most commonly on ILX. This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered.
Common Causes of P0171
- •Vacuum or intake air leak (cracked hose, gasket, or PCV system)
- •Dirty or failing mass airflow (MAF) sensor
- •Weak fuel pump or restricted fuel filter
- •Clogged or dirty fuel injectors
- •Faulty or aged upstream oxygen sensor
- •Leaking intake manifold gasket
- •Low fuel pressure or failing fuel pressure regulator
- •Exhaust leak ahead of the oxygen sensor
P0171 on Acura by Model
Acura ILX(1 issue)
- In-Tank Low-Pressure Fuel Pump Impeller Failure Causing Engine Stall2013-2022
The Denso-supplied in-tank fuel pump module fitted across virtually the entire ILX production run uses an impeller that was molded with insufficient density and inadequately dried. The impeller absorbs fuel, swells, and interferes with the pump body. The pump then fails to deliver pressure - typically presenting first as a long crank or a hard start, then progressing to an engine stall that can happen at road speed with no warning and no restart. The ILX coverage was expanded twice: an initial 2019-2020 campaign (21V215, itself an expansion of ) was later broadened to cover 2013-2023 ILX under 23V858, so this spans every powertrain the car was sold with - 2.0 automatic, 2.4 manual, hybrid, and 2.4 DCT alike.
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View P0171 across all makes →Frequently Asked Questions
What does P0171 mean on Acura?▼
P0171 stands for "System Too Lean (Bank 1)." This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. On Acura specifically, this code is documented across 1 model.
What causes P0171 on Acura vehicles?▼
Common causes on Acura: Vacuum or intake air leak (cracked hose, gasket, or PCV system), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter, Clogged or dirty fuel injectors, Faulty or aged upstream oxygen sensor. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0171 on a Acura?▼
Repair costs vary widely depending on the root cause and specific Acura model.
Which Acura models have P0171 documented?▼
Au7o has documented P0171 on 1 Acura model: ILX.