P0171 on Buick
System Too Lean (Bank 1)
P0171 on Buick vehicles indicates system too lean (bank 1). Au7o has documented this code across 3 Buick models — most commonly on Encore, LeSabre, Park Avenue. 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. Typical repair costs on Buick range from $150 to $1,200, depending on the specific model and root cause.
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 Buick by Model
Buick Encore(1 issue)
- PCV / Camshaft Cover Diaphragm Failure (1.4L Turbo) - "Tea Kettle" Whistle2013-2021
The 1.4L turbocharged engine (LUV/LUJ family) used in the first-generation Encore is prone to a ruptured PCV pressure-regulator diaphragm built into the plastic camshaft (valve) cover. When the diaphragm cracks, unmetered air enters the intake, producing a loud high-pitched whistle or squeal that owners describe as a boiling tea kettle under the hood, along with rough idle and stalling at stops. GM acknowledged the defect with Special Coverage N202299080, extending warranty on the PCV/camshaft cover to 10 years / 120,000 miles for certain 2014 Encore (and related Cruze/Sonic/Trax) vehicles.
Buick LeSabre(1 issue)
- LeSabre 3800 V6 Lower Intake Manifold (LIM) Gasket Leak1995-2005
Same 3800 V6 LIM-gasket failure mode as Park Avenue — extremely widespread in 1995-2005 LeSabres. Coolant migrates past degraded plastic-and-rubber gasket into the valley, contaminating engine oil. Owners commonly first notice low coolant with no visible leak; by the time milky oil appears, bearings may already be damaged.
Buick Park Avenue(1 issue)
- Park Avenue 3800 V6 Lower Intake Manifold (LIM) Gasket Leak1995-2005
The 3800 Series II (and early III) V6 in Park Avenue, LeSabre, Riviera, Regal, Lucerne — and shared Pontiac Bonneville/Grand Prix, Olds 88/LSS, Chevy Monte Carlo/Impala — suffers infamous lower intake manifold gasket failure. Plastic intake material softens under coolant exposure (especially Dex-Cool); gasket erodes and leaks coolant into the lifter valley, mixing with oil. Catastrophic if undetected.
Looking for P0171 on a different make?
View P0171 across all makes →Frequently Asked Questions
What does P0171 mean on Buick?▼
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 Buick specifically, this code is documented across 3 models.
What causes P0171 on Buick vehicles?▼
Common causes on Buick: 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 Buick?▼
Repair costs on Buick range from $150 to $1,200, depending on the specific model and root cause.
Which Buick models have P0171 documented?▼
Au7o has documented P0171 on 3 Buick models: Encore, LeSabre, Park Avenue.