P0174 on Mazda
System Too Lean (Bank 2)
P0174 on Mazda vehicles indicates system too lean (bank 2). Au7o has documented this code across 3 Mazda models — most commonly on CX-5, Mazda3, RX-8. 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 Mazda range from $300 to $5,000, 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 Mazda by Model
Mazda CX-5(2 issues)
- Carbon Buildup on Intake Valves (Skyactiv)2013-2023
Direct-injection Skyactiv engines accumulate carbon deposits on intake valves due to oil vapors from the PCV system. Without port injection to clean valves, carbon can fuse to valve surfaces over time, typically appearing around 65,000+ miles.
- Excessive Engine Oil Consumption2013-2022
Defective valve stem seals allow oil to leak into combustion chambers, causing excessive oil consumption and potential catastrophic engine failure if oil levels drop critically low. Issue primarily affects 2013-2014 models with resurgence in 2021-2022.
Mazda Mazda3(1 issue)
- Carbon Buildup on Direct Injection Intake Valves2012-2025
SkyActiv direct-injection engines lack port injection to wash intake valves, causing carbon deposits to accumulate over time. Carbon buildup restricts airflow, causing rough idle, misfires, and power loss. Typically becomes noticeable around 60,000-80,000 miles.
Mazda RX-8(1 issue)
- Apex Seal Failure / Compression Loss2004-2012
The Renesis rotary engine in the RX-8 is infamous for apex seal wear and failure, leading to catastrophic compression loss. Apex seals maintain the combustion chamber seal between the rotor and housing. Heat, carbon deposits, and inadequate lubrication cause seals to wear, chip, or break. Compression testing below 6.5 kg/cm2 indicates rebuild is needed. This is the single most common and feared RX-8 issue.
Looking for P0174 on a different make?
View P0174 across all makes →Frequently Asked Questions
What does P0174 mean on Mazda?▼
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 Mazda specifically, this code is documented across 3 models.
What causes P0174 on Mazda vehicles?▼
Common causes on Mazda: 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 Mazda?▼
Repair costs on Mazda range from $300 to $5,000, depending on the specific model and root cause.
Which Mazda models have P0174 documented?▼
Au7o has documented P0174 on 3 Mazda models: CX-5, Mazda3, RX-8.