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Warning Powertrain · P0174

P0174 — System Too Lean (Bank 2)

Bank 2 is running with too much air or too little fuel, and the computer has run out of room to add fuel to correct it.

How to diagnose See repair cost
Can I drive?
Drive with caution

Fix soon — limit driving

Repair cost

$150–$800

DIY from $20

DIY difficulty

Moderate

If you do it yourself

Urgency

Within 1–2 weeks

Before bigger damage

Common symptoms

  • Check engine light on
  • Rough idle and hesitation
  • Reduced power and economy
  • Surging at cruise

Common causes, ranked by likelihood

Based on typical diagnoses for P0174. Work from the most likely cause down before replacing expensive parts.

Vacuum or intake air leak 40%
Dirty or failing MAF sensor 25%
Weak fuel delivery 15%
Faulty PCV system 12%
Stuck-open EVAP purge valve 8%

How to diagnose it

  1. Check fuel trims — P0174 with P0171 usually means a shared cause like the MAF or fuel delivery rather than a single vacuum leak.
  2. Smoke-test the intake to find vacuum leaks affecting both banks.
  3. Clean or test the MAF sensor.
  4. Verify fuel pressure and volume.
  5. Inspect PCV and purge valves.

DIY vs shop cost

DIY Moderate

$20–$250

Parts, if you do the labour yourself.

Common parts
Start the DIY fix
Shop

$150–$800

Parts + labour at an independent shop.

Make-specific notes

Ford

P0171 and P0174 together on Ford V8s often point to the MAF sensor or a failed PCV/intake gasket affecting both banks.

P0174 questions, answered

What does it mean if I have both P0171 and P0174?

Both banks are lean, which points to a cause shared by the whole engine — most often a dirty MAF sensor or weak fuel delivery — rather than a single localized vacuum leak.

Can I keep driving with P0174?

For a short time, yes, but fix it promptly. Running lean can trigger misfires and damage the catalytic converter over time.