OBD-II trouble code
P0174: System Too Lean (Bank 2)
The engine computer detected that Bank 2 is running with too much air or too little fuel. Same condition as P0171, but on the opposite side of a V-configured engine. Only applies to V engines.
Quick facts
- System
- Powertrain
- Category
- Fuel and Air Metering
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $50 – $1,000
- DIY difficulty
- Intermediate DIY
What does P0174 mean?
P0174 is the Bank 2 equivalent of P0171. The engine control module (ECM) monitors the air-fuel mixture using oxygen sensors and adjusts fuel injection to keep combustion ideal. "Lean" means there is too much air relative to fuel. When long-term fuel trim on Bank 2 climbs past roughly +10% to +25% for an extended period (the exact threshold varies by manufacturer), the ECM sets P0174.
Bank 2 refers to the side of the engine that does not contain cylinder 1. P0174 only applies to V-configuration engines (V6, V8, etc.) and a small number of horizontally-opposed and inline configurations with dual oxygen sensor banks. Inline engines with a single bank cannot set P0174.
It's not unusual to see P0171 and P0174 together on aging V engines, especially when the cause is a shared component — a failing MAF sensor, a weak fuel pump, or a vacuum leak in a centrally-located component like the intake manifold gasket. If only P0174 is set, the cause is more likely isolated to the Bank 2 side: a Bank 2 vacuum leak, a Bank 2 fuel injector, or a Bank 2 oxygen sensor.
Common causes
- Vacuum leak isolated to the Bank 2 intake side (cracked hose, intake manifold gasket)
- Dirty or failing mass airflow (MAF) sensor — if also causing P0171, the MAF is shared and affects both banks
- Weak fuel pump or clogged fuel filter reducing fuel pressure to both banks
- Leaking or clogged Bank 2 fuel injector
- Exhaust leak upstream of the Bank 2 upstream oxygen sensor
- Faulty Bank 2 upstream oxygen sensor reading lean
- Bank 2 intake manifold gasket leak
- Stuck-open EVAP purge valve drawing unmetered air
Symptoms
- Check engine light is on
- Rough or unstable idle
- Hesitation on acceleration
- Occasional misfire under load
- Reduced fuel economy
- Possible stalling at idle in severe cases
Diagnostic steps
- 1.Check whether P0171 is also set. If both codes are present, the cause is shared between banks — start with the MAF sensor, fuel pressure, and centrally-located vacuum components.
- 2.If only P0174 is set, focus on Bank 2-specific components: the Bank 2 intake side hoses, Bank 2 injectors, and Bank 2 oxygen sensor.
- 3.Scan fuel trims for both banks. If Bank 2 LTFT is significantly higher than Bank 1, the problem is isolated to Bank 2.
- 4.Smoke test or use carb cleaner around Bank 2 intake joints to find vacuum leaks.
- 5.Test the Bank 2 upstream oxygen sensor signal pattern.
- 6.Check fuel pressure against manufacturer specification.
Repair cost
$50 – $1,000
A Bank 2 vacuum hose repair is $30 to $150. Intake manifold gasket replacement on the Bank 2 side runs $300 to $700. MAF sensor replacement is $150 to $450. Bank 2 oxygen sensor replacement is $150 to $400. Fuel pump replacement is the most expensive likely outcome at $400 to $1,000.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with vacuum leak repair preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.