P0174 on Porsche
System Too Lean (Bank 2)
P0174 on Porsche vehicles indicates system too lean (bank 2). Au7o has documented this code across 4 Porsche models — most commonly on 718 Boxster, 911, Boxster. P0174 means the engine computer detected that the air-fuel mixture on Bank 2 (the side of the engine with cylinder 2) is running too lean — too much air relative to fuel. The computer monitors this through the oxygen/air-fuel sensors and fuel trims; when it has to add a large amount of extra fuel to compensate and still can't reach the target, it flags the mixture as too lean. A lean condition can cause rough idle, hesitation, or misfires, and over time can raise combustion temperatures. Because it's Bank 2 specific, an unmetered air leak on that bank or a fuel delivery shortfall is typical. Typical repair costs on Porsche range from $400 to $1,500, depending on the specific model and root cause.
Common Causes of P0174
- •Vacuum or intake air leak (hoses, gaskets, PCV)
- •Dirty or failing mass airflow (MAF) sensor
- •Weak fuel pump or restricted fuel filter (low fuel pressure)
- •Clogged or underperforming fuel injectors
- •Leaking intake manifold or throttle body gasket
- •Faulty or contaminated oxygen / air-fuel sensor
- •Exhaust leak upstream of the oxygen sensor
- •Stuck-open EGR valve
P0174 on Porsche by Model
Porsche 718 Boxster(1 issue)
- Air-Oil Separator (AOS) Failure Causing Oil Ingestion and Smoke2017-2025
The air-oil separator (crankcase breather/oil separator) on the turbocharged flat-four 718 can fail, causing excessive crankcase vacuum that draws engine oil into the intake. Owners report white/blue smoke (especially at startup or under acceleration), an oil smell, fouled spark plugs, and fuel-trim/check-engine faults. In severe cases the failing AOS has drawn paper-filter debris and oil that blocked the variable-cam (VarioCam) oil passages, requiring major engine teardown. Track-driven cars are especially prone because the stock unit cannot handle the load, risking oil ingestion that can hydro-lock or damage a cylinder.
Porsche 911(1 issue)
- Air-Oil Separator (AOS) Failure1999-2008
The AOS diaphragm on M96/M97 engines ruptures over time, causing unmetered air leaks into the intake manifold and excessive oil consumption. The failed AOS allows oil vapor to be drawn directly into the intake system rather than being separated and returned to the crankcase. This leads to rich running, fouled spark plugs, and smoke from the exhaust.
Porsche Boxster(1 issue)
- Air-Oil Separator (AOS) Diaphragm Failure1997-2008
The AOS on the Boxster M96 engine suffers the same diaphragm rupture as the 911 variant. The failed diaphragm allows unmetered air into the intake and oil vapor to bypass the separation system, causing oil consumption, rough idle, and fouled spark plugs.
Porsche Cayman(1 issue)
- Air-Oil Separator (AOS) Failure2006-2012
The Cayman M97 engine shares the same AOS weakness as the Boxster and 911. The diaphragm ruptures, causing vacuum leaks, excessive oil consumption, and fouled spark plugs. The mid-engine layout makes the AOS moderately accessible for replacement.
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View P0174 across all makes →Frequently Asked Questions
What does P0174 mean on Porsche?▼
P0174 stands for "System Too Lean (Bank 2)." P0174 means the engine computer detected that the air-fuel mixture on Bank 2 (the side of the engine with cylinder 2) is running too lean — too much air relative to fuel. The computer monitors this through the oxygen/air-fuel sensors and fuel trims; when it has to add a large amount of extra fuel to compensate and still can't reach the target, it flags the mixture as too lean. A lean condition can cause rough idle, hesitation, or misfires, and over time can raise combustion temperatures. Because it's Bank 2 specific, an unmetered air leak on that bank or a fuel delivery shortfall is typical. On Porsche specifically, this code is documented across 4 models.
What causes P0174 on Porsche vehicles?▼
Common causes on Porsche: Vacuum or intake air leak (hoses, gaskets, PCV), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter (low fuel pressure), Clogged or underperforming fuel injectors, Leaking intake manifold or throttle body gasket. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0174 on a Porsche?▼
Repair costs on Porsche range from $400 to $1,500, depending on the specific model and root cause.
Which Porsche models have P0174 documented?▼
Au7o has documented P0174 on 4 Porsche models: 718 Boxster, 911, Boxster, Cayman.