P0174 Code: Honda Accord (2018-2023) - Causes, Symptoms & Fixes

P0174 Diagnostic Guide for 2018–2023 Honda Accord

Important data note:

• Data provided: Owner complaints for this specific make/model/year/issue: None found in the dataset.
• Recalls: No recalls found in NHTSA database for this make/model/year.
• Data limitation: The numbers above come from the provided dataset. They do not replace broader vehicle history checks. Use this guide as a diagnostic help, not a guarantee of results.

CODE MEANING AND SEVERITY

• Code: P0174 — System Too Lean (Bank 2)
• What it means: The engine control module (ECM) detects a lean air-fuel mixture on Bank 2 (the “other” bank in the engine’s setup). In practice, this means the ECM is seeing signs that there’s too much air relative to fuel on that bank, or it’s failing to add enough fuel. The condition is usually reflected in fuel trim data (long-term and short-term trims staying positively lean).
• Severity: Moderate. A lean condition can cause drivability issues (hesitation, reduced power, rough idle) and, if persistent, may stress the catalytic converter or cause overheating. If the problem is severe, you’ll typically see the check engine light (MIL) on and possibly intermittent power loss. In many cases, multiple related codes or live data will guide you to the root cause.

COMMON CAUSES ON HONDA ACCORD (2018–2023)

Note: These are common causes seen across many Honda Accord setups (including 1.5T, 2.0T, and hybrid variants). Specific engines may highlight different culprits, but the following are frequent sources of P0174.

• Vacuum leaks and PCV system leaks
  • Cracked or disconnected vacuum hoses, damaged intake boot, faulty PCV valve, or degraded intake manifold gaskets.
  • Turbocharged variants (1.5T/2.0T) can be especially sensitive to PCV hose and intake leaks around the turbocharger plumbing.
• Mass Air Flow (MAF) sensor issues
  • Dirty or failing MAF sensor causing incorrect air measurement. Contamination from oil, dirt, or cobwebs can skew readings.
• Manifold Absolute Pressure (MAP) sensor issues
  • Faulty MAP sensor or wiring can misreport air pressure, affecting fuel trim calculations.
• Oxygen sensors (O2 sensors)
  • Faulty upstream O2 sensor (or occasionally downstream) can misreport exhaust composition, leading to incorrect fuel trimming.
• Fuel delivery problems
  • Low fuel pressure or insufficient fuel supply (weak pump, clogged fuel filter where equipped, or a failing fuel pressure regulator in some designs).
• Exhaust and emissions-related issues
  • EGR valve stuck open/partially open, creating additional intake air and a leaning condition.
  • Excessive exhaust backpressure can influence readings indirectly in some configurations.
• EVAP and vapor leaks
  • Small leaks or purge valve issues can cause intermittent lean readings, especially under certain drives.
• Intake leaks and gasket issues
  • Leaks around the intake manifold gasket or throttle body gasket can introduce unmetered air.
• Injectors and fuel delivery cleanliness
  • Clogged or dirty injectors can cause uneven fuel delivery and lean readings if one bank isn’t getting enough fuel.
• Engine mechanical symptoms (less common)
  • Low compression or ignition misfires can sometimes present with lean-type fuel-trim symptoms, particularly if the ECM compensates to maintain idle stability.

SYMPTOMS TO EXPECT WITH P0174

• Check Engine Light (MIL) is on or intermittently illuminated.
• Rough idle or stumble when idling or at low RPM.
• Hesitation, slow acceleration, or reduced engine power under load.
• Poor fuel economy (lower miles per gallon).
• In some cases, the vehicle may run normally once at speed, with the problem showing up mainly under acceleration or at certain temperatures.
• In test data, P0174 can occur in conjunction with P0171 (Bank 1 lean) if multiple banks show lean conditions or if the engine’s overall condition leads to systemic lean readings.

DIAGNOSTIC STEPS (GUIDE)

Use a code scanner with live data (freeze frame, fuel trims, sensor readings) and, if possible, a smoke machine for vacuum testing.

Step 1: Confirm the codes and data

• Read P0174 with freeze-frame data.
• Note long-term fuel trim (LTFT) and short-term fuel trim (STFT) for Bank 2, plus any related codes (e.g., P0171 or P0173 for other banks).
• Record O2 sensor readings (upstream and downstream) and MAF readings at idle and at a stable RPM.

Step 2: Check for obvious vacuum leaks

• Visually inspect vacuum hoses, PCV valve, intake boot, and connections around the intake manifold and turbo plumbing (if equipped).
• Perform a smoke test if available to reveal hidden leaks.
• Repair any cracked hoses, loose clamps, or damaged gaskets.

Step 3: Inspect the MAF and MAP sensors

• Clean the MAF sensor with a proper MAF-safe cleaner if no fault codes point to a failed sensor.
• If MAF readings are wildly inconsistent with engine speed or IVO (intake volume), replace the MAF sensor.
• Check MAP sensor readings: compare the MAP sensor’s output to manifold pressure at key RPMs. Replace if readings are out of spec or if wiring is damaged.

Step 4: Examine O2 sensors

• Test upstream O2 sensor(s) for proper response time and switching between lean and rich. A slow or “lazy” upstream sensor can cause incorrect fuel trimming.
• If upstream O2 sensor values stay stuck lean after the engine warms up, consider replacement. Check downstream O2 sensor for proper catalytic converter function with data.

Step 5: Assess fuel delivery

• Measure actual fuel pressure with a fuel pressure gauge and compare to the factory specification for the engine variant.
• Check for signs of a weak fuel pump, collapsing fuel lines, or a blocked fuel filter (if equipped). Replace the fuel pump assembly or filter as needed.
• Inspect fuel injectors for spray pattern and clogging; consider injector cleaner or professional cleaning if performance is suspect.

Step 6: Check EGR system (if equipped)

• Inspect EGR valve for carbon buildup or improper operation (sticking open). A faulty EGR valve can cause lean conditions in some systems.

Step 7: Inspect the EVAP system

• Check purge valve and hoses for sticking or leaks. EVAP issues can sometimes register as lean conditions under certain conditions.

Step 8: Check for any other engine problems

• Look for misfire-related codes (P0300 series) that might accompany lean readings.
• Perform a compression test if mechanical issues are suspected (low compression can lead to lean symptom interpretations under load).

Step 9: Clear codes and re-test

• After performing repairs, clear codes and perform a road test under varying loads and temperatures.
• Recheck LTFT/STFT and confirm P0174 does not reappear.

RELATED CODES

• P0171: System Too Lean (Bank 1)
• P0173: System Too Lean (Bank 2) (alternate designation in some scans)
• P0172, P0175: System Too Rich (Bank 1 or Bank 2) — less common with P0174 but can appear if fuel trim oscillates
• Other helpful related codes to consider during diagnosis: P0101 (Mass/Volume Air Flow Circuit Range/ Performance), P0120–P0124 (Throttle Position Sensor range/performance), P0130–P0133 (O2 sensor circuits) and P0300 (random/multiple cylinder misfire)

REPAIR OPTIONS AND COSTS (2025 PRICES)

Notes:

• Prices vary by region, shop, engine variant (1.5T, 2.0T, hybrid), and labor rates. The ranges below are typical for the US in 2025 and include parts plus estimated labor.
• Labor times are approximate and depend on the exact root cause and access. Always obtain a written estimate before major work.

A. Vacuum leaks and PCV system

• Parts: PCV valve, hoses, clamps, gaskets as needed
• Typical cost: Parts $5–$60; Labor 0.5–2.0 hours
• Estimated total: $75–$200

B. MAF sensor cleaning or replacement

• Cleaning (DIY): $0–$5 (cleaner)
• Replacement sensor: $100–$260 (parts)
• Labor: 0.3–1.0 hour
• Estimated total: $70–$300

C. MAP sensor

• Parts: MAP sensor $60–$160
• Labor: 0.2–0.5 hour
• Estimated total: $80–$230

D. O2 sensors (upstream)

• Parts: $80–$250 per sensor
• Labor: 0.5–1.0 hour
• Estimated total: $200–$450

E. Fuel delivery system diagnostics and repair

• Fuel pressure test tool usage and possible pump/line repair
• Parts: Fuel pump assembly $200–$700 (if needed); fuel filter if applicable $20–$60
• Labor: 1–3 hours
• Estimated total: $350–$1000

F. EGR valve

• Parts: EGR valve $150–$400
• Labor: 0.5–1.5 hours
• Estimated total: $250–$650

G. EVAP purge system

• Parts: Purge valve $60–$200
• Labor: 0.3–1.0 hour
• Estimated total: $120–$350

H. Intake manifold gasket (less common, higher cost)

• Parts: Gasket set or intake gasket
• Labor: 3–6 hours
• Estimated total: $600–$1800

I. Injectors (cleaning or replacement)

• Cleaning: $0–$50 (DIY or shop kit)
• Replacement injectors (if needed): $200–$500 per injector
• Labor: 0.5–2.0 hours
• Estimated total: $200–$1500 (depending on number of injectors and loom access)

J. General electrical/connectors

• Parts: Connectors, harness pins if damaged
• Labor: 0.2–1.0 hour
• Estimated total: $120–$300

Total cost range (typical scenarios)

• Quick vacuum/MAF-related fixes: $100–$300
• Sensor-related fixes (MAF/MAP/O2): $150–$500
• Fuel delivery or EVAP/EGR related: $250–$1000
• Major mechanical fixes (manifold gasket, injector service): $600–$1800 or more
• If multiple issues exist or labor rates are high, total can exceed $2,000

DIY VS PROFESSIONAL

• Do-it-yourself (DIY) suitable tasks:
  • Inspect and replace cracked vacuum hoses
  • Replace PCV valve
  • Clean MAF sensor (careful not to damage delicate elements) or replace if faulty
  • Check visually for loose connections and clean electrical connectors
  • Basic fuel pressure tests with guidance (if you have the right tools)
  • Simple EVAP purge valve replacement (if easily accessible)
• Tasks better left to a professional:
  • Accurate fuel pressure testing and diagnosing fuel delivery problems
  • Smoke testing for vacuum leaks (highly effective for pinpointing leaks)
  • EGR system diagnosis and cleaning/removal
  • Intake manifold gasket replacement
  • Injectors cleaning or replacement
  • Complex wiring harness or PCM/software updates
• Safety and warranty:
  • Fuel system work and electrical sensor work can pose safety risks; if you’re unsure, seek professional help.
  • When dealing with turbo systems (1.5T/2.0T), high-boost components require careful handling.

PREVENTION

• Regular maintenance reduces lean-condition risk
  • Replace air filters on schedule; a dirty filter can indirectly affect air measurement and engine breathing.
  • Replace PCV valve at recommended intervals; inspect hoses for cracks.
  • Keep MAF sensor clean; avoid oil contamination on filters near the MAF.
  • Use good quality gasoline and stay up to date with manufacturer-recommended fuel.
  • Regularly inspect vacuum hoses and intercooler/turbo system plumbing (for 1.5T/2.0T) for leaks or loose clamps.
  • Periodically inspect the EVAP system for leaks or failed purge components.
• Proactive diagnostics
  • If LTFT starts riding high on one bank (e.g., consistently +20% to +40%), address vacuum leaks and sensor accuracy before fuel trim deviation worsens.
  • If you notice a degraded fuel economy or rough idle, address lean indicators early to avoid potential catalyst damage.

Final notes

• This guide reflects the provided data: no recalls and no specific complaints dataset for P0174 in 2018–2023 Honda Accord. No recalls found in NHTSA database. Data limitations mean the guide emphasizes general diagnosis and common causes rather than any model-year-specific defect notices.
• Always start with a realistic baseline (scan data, testing, and road testing) before replacing multiple parts. Lean conditions can be caused by a combination of issues, and addressing the simplest, most probable cause first often yields the best results.

If you’d like, tell me which Accord engine you have (1.5T, 2.0T, or hybrid) and any symptoms you’re observing (idle, acceleration, fuel economy, any codes besides P0174). I can tailor the diagnostic steps, data checks, and cost estimates to your exact configuration.