P0174 Code: System Too Lean (Bank 2)

The P0174 trouble code means your engine is running too lean on Bank 2. “Too lean” = the PCM/ECM is adding fuel because it believes there’s extra air, not enough fuel, or a sensor reading problem affecting Bank 2.

Often: Vacuum Leak MAF / Intake Fuel Pressure Fuel Trim Diagnosis
On this page
  1. What P0174 Means
  2. What “Bank 2” Means
  3. Symptoms
  4. Most Common Causes
  5. How to Diagnose (Step-by-Step)
  6. Best Fixes (Most Effective Repairs)
  7. Repair Cost Estimates
  8. FAQs

What Does P0174 Mean?

Code
P0174
Definition
System Too Lean (Bank 2)
System
Fuel / Air Metering
Severity
Moderate (can become serious if ignored)
Common Cause
Unmetered air leak affecting Bank 2 or shared intake air measurement

Your engine computer monitors oxygen sensor feedback and uses fuel trims to keep the air-fuel ratio on target. When the system must add fuel beyond a normal range for Bank 2, it sets P0174.

What Does “Bank 2” Mean?

Bank 2 is the side of a V-style engine (V6/V8) that does not contain cylinder #1. Inline engines (many 4-cylinders) usually have only one bank—so you typically won’t see P0174 on a true single-bank setup.

Common pattern: If you have P0171 + P0174 together, suspect a shared cause like a vacuum leak after the MAF, a dirty/failing MAF sensor, or low fuel pressure.

Symptoms of P0174

  • Check Engine Light (CEL)
  • Rough idle (especially when cold)
  • Hesitation on acceleration
  • Reduced power / sluggish response
  • Misfire codes may appear (P0300–P030x)
  • Sometimes: surging or stalling at idle

Most Common Causes of P0174

1) Vacuum Leaks / Unmetered Air (Most Common)

  • Cracked vacuum hose, PCV hose, or intake tube
  • Intake manifold gasket leak (may affect one bank more than the other)
  • Brake booster hose leak
  • EVAP purge valve stuck open (can act like a vacuum leak)

2) Dirty or Faulty MAF Sensor

If the MAF under-reports airflow, the PCM commands too little fuel and both banks may trend lean. P0174 may appear alone or with P0171.

3) Fuel Delivery Problems

  • Low fuel pressure (pump, filter restriction, regulator issues)
  • Restricted injectors (sometimes bank-specific)
  • Fuel contamination

4) Exhaust Leak Upstream of Bank 2 Sensor

Exhaust leaks before the upstream O2 sensor can draw in outside air and mimic a lean condition.

5) Oxygen Sensor / Wiring Fault (After Testing)

O2 sensors can fail, but they’re not the first place to start. Verify airflow leaks and fuel delivery first.

How to Diagnose P0174 (Step-by-Step)

  1. Scan for related codes (P0171, P0101, P0300, EVAP purge codes, etc.).
  2. Compare fuel trims (STFT/LTFT) for Bank 1 vs Bank 2.
    • Only Bank 2 trims high: suspect bank-specific vacuum leak, injector restriction, or exhaust leak on Bank 2.
    • Both banks high: suspect MAF, intake leak after MAF, or fuel pressure issue.
  3. Inspect intake system (air tube/boots/clamps) and vacuum hoses.
  4. Smoke test for vacuum leaks (fastest way to confirm).
  5. Clean the MAF sensor using MAF cleaner and recheck trims.
  6. Verify fuel pressure under load if trims remain high.
  7. Check for exhaust leaks near Bank 2 manifold/header area.
If the Check Engine Light is flashing: an active misfire is occurring. Continued driving can damage the catalytic converter.

How to Fix P0174 (Most Effective Repairs)

Fix When it makes sense
Repair vacuum leak (hoses, PCV, intake gasket, intake boot) Bank 2 trims high at idle; smoke test confirms leak; hissing/whistling present
Clean/replace MAF sensor Both banks trend lean; MAF readings abnormal; intake plumbing checks out
Fuel system repair (pressure/regulator/pump, injector service) Lean under load; low fuel pressure; injector balance issues
Fix exhaust leak upstream of Bank 2 O2 sensor Soot marks/ticking; lean readings inconsistent; Bank 2-specific symptoms
Replace O2 sensor (after testing) Sensor response tests fail; heater/wiring faults present

P0174 Repair Cost Estimates

Repair Typical Range
Vacuum hose / clamp repair$10 – $100
Intake manifold gasket repair$250 – $900+
MAF cleaning$10 – $25
MAF replacement$80 – $300+
Smoke test diagnosis$80 – $200
Injector cleaning/service$80 – $250
Fuel pump / pressure issue$250 – $1,200+

FAQs

Is P0174 serious?

It can be. Mild lean conditions may be drivable short-term, but prolonged lean operation can lead to misfires, overheating, and catalytic converter stress. Diagnose soon.

Why do I have P0171 and P0174 together?

When both banks are lean, the cause is often shared: a vacuum leak after the MAF, a dirty/failing MAF sensor, or low fuel pressure affecting the entire engine.

What’s the most common fix for P0174?

Finding and repairing unmetered air (vacuum leak) is the most common fix, especially if trims are worse at idle.

Related pages:
P-Codes Hub • P0171 (Bank 1 Lean) • Code Library (Search) • How to Read OBD-II Trouble Codes