What does the P0174 code mean?

P0174 means System Too Lean on Bank 2. The engine is taking in more air than the fuel system can match on the bank of cylinders that does not include cylinder 1. The computer added the most extra fuel it is allowed to (long-term fuel trim past about +25 percent) and still measured a lean mixture, so it sets the code. It appears on V6, V8 and boxer engines, and on inline-sixes that report two banks (such as BMW's M54, N52 and N54, where cylinders 4-6 are bank 2). Four-cylinder engines have a single bank.

What causes a P0174 lean code?

Most often an unmetered air leak: a cracked vacuum hose, a leaking intake manifold gasket, or a loose PCV connection on the Bank 2 side. Other causes are a dirty MAF sensor reading low, weak fuel pressure from a tired pump or clogged filter, dirty or leaking Bank 2 injectors, or an exhaust leak fooling the upstream O2 sensor. If P0171 is set alongside P0174, suspect a shared cause such as the MAF, fuel pressure, or a big central vacuum leak rather than a single-bank fault.

Is it safe to drive with a P0174 code?

For short distances, yes. Avoid heavy load and sustained high RPM. A lean mixture raises combustion temperatures, which over time can damage the catalytic converter and exhaust valves and may cause misfires. Treat it as a fix-within-a-couple-of-weeks issue, not an emergency, unless the car is stalling or the light is flashing.

Which bank is Bank 2 and how do I know which cylinders are affected?

Bank 2 is the side of the engine that does not contain cylinder number 1. Which physical side that is depends on how the manufacturer numbers the cylinders: on the transverse Toyota 2GR-FE V6, for example, bank 2 is the front bank facing the radiator. Confirm the cylinder 1 location in the service data before you start. The fix is usually on that physical bank: its vacuum lines, intake gasket, injectors, or upstream O2 sensor.

How much does it cost to fix P0174?

Cheap fixes are common. Cleaning a MAF sensor, replacing an air filter, or refitting a loose vacuum hose can cost around 30 euros or less. A vacuum hose or gasket replacement typically runs 65 to 260 euros with labour, a PCV valve 40 to 200 euros, and the worst case, a fuel pump, 200 to 700 euros.

P0174: System Too Lean (Bank 2)

Quick Answer

Safe to drive (short-term)

P0174 means the engine is running too lean on Bank 2, the cylinder bank that does not contain cylinder 1. It appears on V6, V8 and boxer engines, and on inline-six engines whose engine management splits the cylinders into two banks with an upstream oxygen sensor each, such as BMW's M54, N52 and N54. The computer added the maximum extra fuel it can (long-term fuel trim past roughly +25 percent) but still measured too much air against the ideal 14.7:1 ratio. The most common cause is an unmetered air leak: a cracked vacuum hose or leaking gasket. The cheapest fixes, a MAF clean or a split vacuum hose, can cost under 100 euros; a gasket or PCV repair runs roughly 40 to 260 euros.

Severity: Moderate · Fuel System
Estimated repair cost: From €30 to €700+, varies by vehicle

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What does P0174 mean?

P0174 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0174 and illuminates the check engine light.

Where it is on the car

Air filter box
Mass airflow sensor (MAF)
Throttle body and throttle position sensor
Intake manifold and MAP sensor
Engine (cylinder head)

A lean code usually means extra air is getting in after the MAF sensor, for example through a leaking intake hose, a cracked vacuum line or a worn manifold gasket. The intake manifold side is the first place to look. A dirty MAF sensor that reads too little air is the other common cause.

What are the symptoms of P0174?

If your vehicle has triggered P0174, you may notice one or more of these symptoms:

Check engine light illuminated, sometimes flashing under load
Rough, high, or unstable idle
Hesitation or stumble during acceleration
Reduced fuel economy
Engine may stall at idle or when coming to a stop
Hissing or whistling sound from a vacuum leak
Slight loss of power and occasional misfire

What causes P0174?

Here are the most common causes of P0174:

Vacuum or intake air leak (cracked hose, leaking intake manifold gasket, loose PCV connection) - lets unmetered air into Bank 2 so the mixture goes lean
: high
Dirty or failing MAF (mass air flow) sensor - under-reports incoming air so the ECU injects too little fuel; if P0171 is also set this is a prime suspect
: high
Weak fuel pump or clogged fuel filter - drops rail pressure so injectors cannot deliver enough fuel to keep up under demand
: medium
Dirty, clogged, or leaking fuel injectors on Bank 2 - restricted spray pattern starves that bank of fuel
: medium
Failing or stuck-open PCV valve - creates a large unmetered vacuum leak that leans out the mixture
: medium
Exhaust leak ahead of the Bank 2 upstream O2 sensor - draws in outside air that the sensor reads as a lean exhaust stream
: low

Is it safe to drive with P0174?

Generally yes, for short-term driving. Short-term driving is safe. Avoid heavy load and high RPM. A lean condition increases combustion temperatures and can damage catalytic converters and exhaust valves if left unaddressed. Fix within a couple of weeks.

How do you diagnose P0174?

Follow these steps to pinpoint the root cause of P0174:

Check whether P0171 is also stored. Both codes together points to a whole-engine cause (dirty MAF, low fuel pressure, or a large central vacuum leak), not a Bank 2-specific fault, so start there
Read short-term and long-term fuel trims on Bank 2 with a scan tool. A long-term trim sustained above about +10 percent shows the bank is correcting for a lean mixture, and the code typically sets near the ECU's limit of around +25 percent; trims that worsen at idle suggest a vacuum leak, trims that worsen under load suggest a fuel-delivery problem
Smoke-test the intake, or spray a small amount of carburettor cleaner around the Bank 2 intake manifold gaskets, vacuum hoses, and PCV connections, watching for an RPM change that pinpoints the leak
Inspect and clean the MAF sensor with dedicated MAF cleaner, then recheck trims; a clogged sensor element is a frequent and cheap fix
Check fuel pressure at the rail with a gauge and compare against the manufacturer specification, both at idle and under a snap-throttle load
Inspect for an exhaust leak ahead of the Bank 2 upstream O2 sensor and verify the sensor is switching correctly before condemning any parts
Compare Bank 1 and Bank 2 trims side by side - a large gap between the two banks isolates the problem to Bank 2 hardware rather than a shared cause

How much does P0174 cost to fix?

Repair costs for P0174 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Fix vacuum leak (replace hose or gasket)	€5–€60	€60–€200	€65–€260	Moderate
Clean or replace MAF sensor	€10–€200	€20–€60	€30–€260	Easy
Replace PCV valve	€10–€80	€30–€120	€40–€200	Easy
Replace fuel pump	€100–€400	€100–€300	€200–€700	Professional
Clean fuel injectors	€15–€50	€50–€150	€65–€200	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

P0174 on specific vehicles

P0174 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0174 on Toyota

Toyota Camry

See Toyota-specific causes & cost

P0174 on Honda

Honda Civic

See Honda-specific causes & cost

P0174 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

P0174 on BMW

BMW 3 Series

See BMW-specific causes & cost

P0174 on Audi

Audi A4

See Audi-specific causes & cost

P0174 on Mercedes-Benz

Mercedes-Benz C-Class

See Mercedes-Benz-specific causes & cost

These codes are often seen alongside P0174 or indicate related issues:

Common questions about P0174

What does the P0174 code mean?: P0174 means System Too Lean on Bank 2. The engine is taking in more air than the fuel system can match on the bank of cylinders that does not include cylinder 1. The computer added the most extra fuel it is allowed to (long-term fuel trim past about +25 percent) and still measured a lean mixture, so it sets the code. It appears on V6, V8 and boxer engines, and on inline-sixes that report two banks (such as BMW's M54, N52 and N54, where cylinders 4-6 are bank 2). Four-cylinder engines have a single bank.
What are the symptoms of P0174?: A lit check engine light, a rough or high idle, hesitation when you accelerate, slightly worse fuel economy, and sometimes a stall at idle. A vacuum leak, the most common cause, often produces a faint hissing or whistling sound under the hood. Many drivers notice no driveability change at all and only find the code on a scan.
What causes a P0174 lean code?: Most often an unmetered air leak: a cracked vacuum hose, a leaking intake manifold gasket, or a loose PCV connection on the Bank 2 side. Other causes are a dirty MAF sensor reading low, weak fuel pressure from a tired pump or clogged filter, dirty or leaking Bank 2 injectors, or an exhaust leak fooling the upstream O2 sensor. If P0171 is set alongside P0174, suspect a shared cause such as the MAF, fuel pressure, or a big central vacuum leak rather than a single-bank fault.
Is it safe to drive with a P0174 code?: For short distances, yes. Avoid heavy load and sustained high RPM. A lean mixture raises combustion temperatures, which over time can damage the catalytic converter and exhaust valves and may cause misfires. Treat it as a fix-within-a-couple-of-weeks issue, not an emergency, unless the car is stalling or the light is flashing.
Which bank is Bank 2 and how do I know which cylinders are affected?: Bank 2 is the side of the engine that does not contain cylinder number 1. Which physical side that is depends on how the manufacturer numbers the cylinders: on the transverse Toyota 2GR-FE V6, for example, bank 2 is the front bank facing the radiator. Confirm the cylinder 1 location in the service data before you start. The fix is usually on that physical bank: its vacuum lines, intake gasket, injectors, or upstream O2 sensor.
How much does it cost to fix P0174?: Cheap fixes are common. Cleaning a MAF sensor, replacing an air filter, or refitting a loose vacuum hose can cost around 30 euros or less. A vacuum hose or gasket replacement typically runs 65 to 260 euros with labour, a PCV valve 40 to 200 euros, and the worst case, a fuel pump, 200 to 700 euros.

Read our detailed guides

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