P0171 on Acura: How to Diagnose & Fix
System Too Lean (Bank 1)
1 Acura model · 1 documented issue · 1 critical
P0171 on Acura by model: symptoms, diagnosis and fix
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.
Common Symptoms
- Engine stalls while driving
- Extended cranking before start
- No-start condition
- Whining or absent fuel pump prime noise at key-on
- Check engine light
- Loss of power under load
How to Fix
Free recall remedy under NHTSA 23V858 (Honda campaign codes KGC/KGD); earlier cars may instead fall under 21V215. Dealers replace the entire fuel pump module at no charge. Owner notification for the expanded campaign was mailed September 2024. Do not pay for a fuel pump on an ILX without first running the VIN - a private-pay pump module replacement typically runs $700-$1,200.
Sources for this issue (3)
P0171 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0171 mean on a 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 it is documented across 1 model: ILX.
What are the most common causes of P0171?
The most common causes of P0171 are: 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. The specific cause varies by vehicle.
How much does it cost to fix P0171 on a Acura?
Repair costs vary widely with the root cause and Acura model; each issue on this page carries its own estimate where one is published.
Looking for P0171 on a different make?
View P0171 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.