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P0174 alone vs. P0171+P0174 together tells a different story. Both codes together usually point to the MAF sensor or a large unmetered air leak after the MAF. P0174 alone suggests a bank-specific issue like an intake manifold gasket leak on that side of the engine. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0174 lean condition traced to MAF sensor or vacuum/intake leak allowing unmetered air (Bank 2)
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0174 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
42%
#1 - Most Likely
Vacuum or Intake Leak (Bank 2 Side)
Cracked intake manifold gaskets, split vacuum hoses, or broken PCV connections allow unmetered air into the engine on the Bank 2 side. On Ford Expedition/F-150 5.4L engines, the plastic upper intake manifold is notorious for cracking at the EGR crossover tube. Spray smoke or carb cleaner around the manifold while the engine idles to locate leaks.
🔩 Part
$10–$300
👨🔧 Labor
$80–$400
⚡ DIY Difficulty
Medium
28%
#2 - Check First
Dirty or Failing MAF Sensor
A contaminated or failing Mass Air Flow sensor underreports incoming air, causing the ECM to think the engine is getting the right amount of fuel when it's actually lean. Cleaning the MAF with dedicated MAF cleaner spray is a $10 fix worth trying before replacement. Never use carburetor cleaner on a MAF - it will destroy the sensing wire.
🔩 Part
$10 (clean) / $80–$300 (replace)
👨🔧 Labor
$0–$60
⚡ DIY Difficulty
Easy
18%
#3 - Less Common
Weak or Failing Fuel Pump
A fuel pump that can't maintain adequate pressure causes a lean condition across the entire engine. The lean condition may only appear at highway speeds or under heavy load. Check fuel pressure at the rail - most gasoline engines require 35–65 psi at idle and should hold pressure for 30+ minutes after shutoff.
🔩 Part
$80–$400
👨🔧 Labor
$100–$300
⚡ DIY Difficulty
Medium–Hard
12%
#4 -
Upstream O2 Sensor (Bank 2, Sensor 1)
A lazy or failed upstream oxygen sensor on Bank 2 can incorrectly report a lean condition. Check the sensor's response time with a live data scan - a healthy sensor should switch between rich and lean several times per second at warm idle. A slow-switching sensor that stays low = lean report even if mixture is fine.
🔩 Part
$30–$120
👨🔧 Labor
$50–$100
⚡ DIY Difficulty
Easy
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Check Freeze Frame and STFT/LTFT Values - Pull live fuel trim data. Short-term (STFT) and long-term (LTFT) fuel trim values above +10% on Bank 2 confirm the PCM is compensating for a lean condition. Values above +25% indicate a significant fuel delivery or air leak problem.
- Inspect for Vacuum Leaks First - Visually check all vacuum hoses on the Bank 2 (passenger) side of the engine. Look for cracked PCV hoses, loose throttle body boots, and cracked intake manifold runners. A smoke machine test finds leaks quickly; carb cleaner spray is a free alternative (exercise caution near ignition sources).
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need