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DTC/P0174

P0174: System Too Lean (Bank 2)

Quick Answer
Moderata GravitàSicuro da guidare (a breve termine)Sistema di alimentazione

P0174 means the engine is running too lean on Bank 2, the cylinder bank that does not contain cylinder 1, so this code only appears on V6, V8, and boxer engines. 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. Most repairs cost under 100 euros.

Costo di riparazione stimatoDa €30 a €700+, varia in base al veicolo

Cosa significa P0174?

P0174 means the engine is running too lean on Bank 2, the cylinder bank that does not contain cylinder 1, so this code only appears on V6, V8, and boxer engines. 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. Most repairs cost under 100 euros.

P0174 è un codice diagnostico di guasto relativo a sistema di alimentazione, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0174 e accende la spia motore.

Quali sono i sintomi di P0174?

Se il tuo veicolo ha attivato P0174, potresti notare uno o più di questi sintomi:

  • 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

Cosa causa P0174?

Ecco le cause più comuni di P0174, ordinate in base alla probabilità che siano la causa del problema:

altaVacuum or intake air leak (cracked hose, leaking intake manifold gasket, loose PCV connection) - lets unmetered air into Bank 2 so the mixture goes lean
altaDirty 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
mediaWeak fuel pump or clogged fuel filter - drops rail pressure so injectors cannot deliver enough fuel to keep up under demand
mediaDirty, clogged, or leaking fuel injectors on Bank 2 - restricted spray pattern starves that bank of fuel
mediaFailing or stuck-open PCV valve - creates a large metered vacuum leak that leans out the mixture
bassaExhaust leak ahead of the Bank 2 upstream O2 sensor - draws in outside air that the sensor reads as a lean exhaust stream

È sicuro guidare con P0174?

In genere sì, per brevi tragitti. 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.

Come si diagnostica P0174?

Segui questi passaggi per individuare la causa principale di P0174:

  1. 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
  2. Read short-term and long-term fuel trims on Bank 2 with a scan tool. A long-term trim above roughly +15 percent confirms the bank is running lean; trims that worsen at idle suggest a vacuum leak, trims that worsen under load suggest a fuel-delivery problem
  3. 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
  4. Inspect and clean the MAF sensor with dedicated MAF cleaner, then recheck trims; a clogged sensor element is a frequent and cheap fix
  5. Check fuel pressure at the rail with a gauge and compare against the manufacturer specification, both at idle and under a snap-throttle load
  6. Inspect for an exhaust leak ahead of the Bank 2 upstream O2 sensor and verify the sensor is switching correctly before condemning any parts
  7. 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

Quanto costa riparare P0174?

I costi di riparazione di P0174 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €5–€60 €60–€200 €65–€260 Moderata
Clean or replace MAF sensor €10–€200 €20–€60 €30–€260 Facile
Replace PCV valve €10–€80 €30–€120 €40–€200 Facile
Replace fuel pump €100–€400 €100–€300 €200–€700 Professionale
Clean fuel injectors €15–€50 €50–€150 €65–€200 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

P0174 su veicoli specifici

P0174 si comporta in modo diverso a seconda del tuo veicolo. Seleziona la tua auto qui sotto per cause specifiche del modello, problemi noti e stime dei costi adeguate:

Toyota

P0174 su Toyota Camry

2007-2024

P0174 only appears on the V6 Camry (2GR-FE), since the four-cylinder is single-bank and triggers P0171 instead. On the V6, the Bank 2 (firewall-side) intake manifold gaskets and the lower intake plenum gaskets can develop vacuum leaks, most commonly on 2007-2011 models. Bank 2 injectors and hoses sit against the firewall, so access is tight and diagnosis takes longer.

Cosa causa P0174 su una Toyota Camry?

Toyota CamryBank 2 intake manifold and plenum gasket vacuum leaks on the 2GR-FE V6
Toyota CamryFirewall-side Bank 2 injectors and vacuum lines are hard to reach, slowing diagnosis
Honda

P0174 su Honda Civic

2006-2024

Nearly every Civic is an inline-four with a single bank, so it sets P0171 rather than P0174. If a scan tool reports P0174 on an inline-four Civic, treat it as suspect and re-scan with a second tool or clear and recheck, because there is no physical Bank 2. The genuine lean causes on a Civic (PCV, vacuum hoses, dirty MAF) still apply, just under P0171.

Cosa causa P0174 su una Honda Civic?

Honda CivicP0174 is effectively impossible on the inline-four (single-bank) Civic
Honda CivicA reported P0174 is usually a scan-tool misread; verify against P0171 instead

Costo di riparazione di P0174 per Honda Civic

Costi stimati per i proprietari di Honda Civicadeguato al ribasso rispetto alla media a causa dei prezzi dei ricambi specifici Honda

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €5–€54 €54–€180 €59–€234 Moderata
Clean or replace MAF sensor €9–€180 €18–€54 €27–€234 Facile
Replace PCV valve €9–€72 €27–€108 €36–€180 Facile
Replace fuel pump €90–€360 €90–€270 €180–€630 Professionale
Clean fuel injectors €14–€45 €45–€135 €59–€180 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Volkswagen

P0174 su Volkswagen Golf

2005-2024

Standard TSI and TFSI Golf models are inline-four and single-bank, so they do not set P0174. Only the VR6-powered Golf R32 has two banks and can trigger it. On the VR6, brittle Bank 2 vacuum lines, the PCV/crankcase breather system, and aged intake manifold seals are the usual leak sources, and ethanol-blended fuel accelerates rubber hose cracking.

Cosa causa P0174 su una Volkswagen Golf?

Volkswagen GolfCracked Bank 2 vacuum lines and PCV/crankcase breather leaks on the VR6 (R32)
Volkswagen GolfNot applicable to standard inline-four TSI/TFSI Golf models

Costo di riparazione di P0174 per Volkswagen Golf

Costi stimati per i proprietari di Volkswagen Golfadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Volkswagen

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €6–€69 €69–€230 €75–€299 Moderata
Clean or replace MAF sensor €12–€230 €23–€69 €35–€299 Facile
Replace PCV valve €12–€92 €35–€138 €46–€230 Facile
Replace fuel pump €115–€460 €115–€345 €230–€805 Professionale
Clean fuel injectors €17–€57 €57–€173 €75–€230 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

BMW

P0174 su BMW 3 Series

2006-2024

The common BMW inline-six engines (N52, N55, B58) are single-bank and set P0171, not P0174. Only the V8 cars, chiefly the S65 in the E90/E92 M3, have a Bank 2 that can throw this code. On the S65, cracked Bank 2 intake-side vacuum lines, a perished crankcase ventilation diaphragm, and ageing rubber boots are the primary lean triggers, and parts and labour run high.

Cosa causa P0174 su una BMW 3 Series?

BMW 3 SeriesBank 2 intake and throttle vacuum leaks on the S65 V8 (E90/E92 M3)
BMW 3 SeriesCrankcase ventilation (CCV) diaphragm failure pulling the V8 lean

Costo di riparazione di P0174 per BMW 3 Series

Costi stimati per i proprietari di BMW 3 Seriesadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici BMW

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €7–€84 €84–€280 €91–€364 Moderata
Clean or replace MAF sensor €14–€280 €28–€84 €42–€364 Facile
Replace PCV valve €14–€112 €42–€168 €56–€280 Facile
Replace fuel pump €140–€560 €140–€420 €280–€980 Professionale
Clean fuel injectors €21–€70 €70–€210 €91–€280 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Audi

P0174 su Audi A4

2005-2024

Four-cylinder TFSI A4 models are single-bank and set P0171; P0174 shows up on the V6 cars such as the 3.0 and 3.2 FSI. On these the PCV/crankcase breather system is a notorious lean source, and the Bank 2 side of the intake manifold and its gaskets crack with age and heat. Carbon build-up on direct-injection valves can worsen the lean reading.

Cosa causa P0174 su una Audi A4?

Audi A4PCV/crankcase breather diaphragm failure on the 3.0/3.2 V6 causing a metered vacuum leak
Audi A4Bank 2 intake manifold seal and vacuum hose cracking with age

Costo di riparazione di P0174 per Audi A4

Costi stimati per i proprietari di Audi A4adeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Audi

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €6–€75 €75–€250 €81–€325 Moderata
Clean or replace MAF sensor €13–€250 €25–€75 €38–€325 Facile
Replace PCV valve €13–€100 €38–€150 €50–€250 Facile
Replace fuel pump €125–€500 €125–€375 €250–€875 Professionale
Clean fuel injectors €19–€63 €63–€188 €81–€250 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Mercedes-Benz

P0174 su Mercedes-Benz C-Class

2005-2024

Four-cylinder C-Class models are single-bank and report P0171; the V6 and V8 variants (M272, M273, M276) can set P0174. On the M272/M273 the intake manifold air-flow control runner and its seals are a known vacuum-leak point on Bank 2, and the crankcase breather (oil separator) diaphragm tears with age, leaning out the mixture.

Cosa causa P0174 su una Mercedes-Benz C-Class?

Mercedes-Benz C-ClassIntake manifold runner/flap seal vacuum leak on the M272/M273 V6 and V8
Mercedes-Benz C-ClassCrankcase breather oil-separator diaphragm tear leaning Bank 2

Costo di riparazione di P0174 per Mercedes-Benz C-Class

Costi stimati per i proprietari di Mercedes-Benz C-Classadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Mercedes-Benz

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Fix vacuum leak (replace hose or gasket) €7–€81 €81–€270 €88–€351 Moderata
Clean or replace MAF sensor €14–€270 €27–€81 €41–€351 Facile
Replace PCV valve €14–€108 €41–€162 €54–€270 Facile
Replace fuel pump €135–€540 €135–€405 €270–€945 Professionale
Clean fuel injectors €20–€68 €68–€203 €88–€270 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Questi codici compaiono spesso insieme a P0174 o indicano problemi correlati:

P0171P0172P0175P0101P0102P0300

Domande frequenti su 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 only appears on V6, V8, and boxer engines because 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. On most transverse (sideways) V6 layouts that is the bank closest to the firewall, but it varies by manufacturer, so confirm 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 tightening a split vacuum hose can be under 30 euros. A vacuum hose or gasket replacement typically runs 60 to 200 euros with labour, a PCV valve 40 to 200 euros, and the worst case (a fuel pump or pressure regulator) 300 to 500 euros. Most P0174 repairs land under 100 euros once the leak is found.

Leggi le nostre guide dettagliate

How to Fix P0174 (Too Lean, Bank 2): Causes and Repair Cost

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How to Fix P0171 (System Too Lean): Causes and Repair Cost

P0171 repair cost runs €50 to €800: a vacuum leak or dirty MAF sensor are the cheapest, common fixes. How to diagnose with fuel trims and fix it yourself.

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