P0171 on Mercury
System Too Lean (Bank 1)
P0171 on Mercury vehicles indicates system too lean (bank 1). Au7o has documented this code across 1 Mercury model — most commonly on Sable. 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 Mercury range from $50 to $350, 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 Mercury by Model
Mercury Sable(1 issue)
- Lean-Condition Codes (P0171/P0174), Rough Idle and Stalling1996-2005
Sable V6s commonly set P0171 and P0174 (system too lean, both banks) together, with rough idle, surging, and stalling. Because both banks read lean, the usual culprits are a dirty/failing mass airflow (MAF) sensor, vacuum leaks, PCV system leaks, or weak fuel delivery. A frequently cited Sable-specific cause is the cam-cover-to-intake vent (PCV) tubes: the plastic angle adapters that join the tubes to the cam covers rot out underneath the bend, creating an unmetered air leak. EGR gasket/valve leaks can also contribute.
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View P0171 across all makes →Frequently Asked Questions
What does P0171 mean on Mercury?▼
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 Mercury specifically, this code is documented across 1 model.
What causes P0171 on Mercury vehicles?▼
Common causes on Mercury: 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 Mercury?▼
Repair costs on Mercury range from $50 to $350, depending on the specific model and root cause.
Which Mercury models have P0171 documented?▼
Au7o has documented P0171 on 1 Mercury model: Sable.