P0171 on Lexus
System Too Lean (Bank 1)
P0171 on Lexus vehicles indicates system too lean (bank 1). Au7o has documented this code across 1 Lexus model — most commonly on NX. 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 Lexus by Model
Lexus NX(1 issue)
- Low-Pressure Fuel Pump Failure Causing Engine Stall (Recall 25V028000)2019
The low-pressure fuel pump inside the fuel tank can fail, cutting fuel supply and stalling the engine — potentially at speed and in traffic. This is the same Denso low-density impeller family of failures that ran across a very large number of Toyota and Lexus products, in which the impeller absorbs fuel, swells, and binds in the pump housing. NHTSA campaign 25V028000 covers 2019 Lexus NX300 alongside the 2018 Camry and 2019 RX350L. Owner notification letters were mailed March 12, 2025, and the campaign numbers are 25LA01 for Lexus and 25TA01 for Toyota. The remedy is replacement of the fuel pump assembly.
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View P0171 across all makes →Frequently Asked Questions
What does P0171 mean on Lexus?▼
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 Lexus specifically, this code is documented across 1 model.
What causes P0171 on Lexus vehicles?▼
Common causes on Lexus: 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 Lexus?▼
Repair costs vary widely depending on the root cause and specific Lexus model.
Which Lexus models have P0171 documented?▼
Au7o has documented P0171 on 1 Lexus model: NX.