P0174 Code: Toyota Camry (2018-2024) - Causes, Symptoms & Fixes

Below is a comprehensive diagnostic guide for P0174 on 2018-2024 Toyota Camry. Note that the provided NHTSA data set in your prompt does not include any P0174 complaints for these model years (the only listed complaint is P0442). There are no recalls listed for this make/model in the provided data. As such, this guide draws on general, defensible automotive knowledge for P0174 on Toyota Camry 2018-2024 and cites no recalls/TSBs from the data you supplied.

CODE MEANING AND SEVERITY

• What the code means:
  • P0174 = System Too Lean (Bank 2) in the OBD-II standard interpretation. On many 4-cylinder Camry engines, there is effectively a single intake bank, so lean conditions can manifest as P0171/P0174 depending on the ECU’s bank mapping. In practical terms, P0174 indicates the engine control system perceives too much air or not enough fuel on the active bank, causing the air-fuel mixture to be lean.
• Severity and risk:
  • Lean running can cause rough idle, hesitation, loss of power, and reduced fuel economy. Prolonged lean conditions raise the risk of catalyst overheating and misfire-related damage to the engine. If the CEL is on and fuel trims remain elevated, diagnosis and repair should be pursued promptly.
• Data limitations:
  • The supplied dataset does not include any P0174 complaints or a direct P0174 case study for the Camry. Use this guide as a general diagnostic framework for P0174 on Camry 2018-2024.

COMMON CAUSES ON TOYOTA CAMRY (2018-2024)

• Vacuum leaks and related air leaks:
  • Cracked or disconnected vacuum hoses, intake boots, or tube seals.
  • PCV valve hose or PCV valve sticking or failing.
  • Intake manifold gasket leaks.
• Air intake and sensing issues:
  • Dirty or faulty Mass Air Flow (MAF) sensor.
  • Dirty or restricted air filter.
  • Air leaks after the MAF (before the throttle body) or around the throttle body.
• Fuel delivery issues:
  • Low fuel pressure (weak fuel pump, restricted fuel filter, failing fuel pressure regulator).
  • Dirty or clogged fuel injectors.
  • Fuel trim issues from a marginal fuel pump or regulator causing under-fueling.
• Engine sensors and control:
  • Upstream (pre-catalytic converter) O2 sensor faulty or drifting out of spec.
  • MAP sensor (if applicable to your engine) providing incorrect readings.
  • EGR system that is stuck open or partially open (can create lean symptoms).
• Exhau st leaks or other sources:
  • Small exhaust leaks before the O2 sensor can fool sensors into reading lean conditions.
• Other possibilities:
  • Faulty spark plugs or ignition misfires (can produce lean-looking short-term data due to misfire dynamics).
  • Engine mechanical issues (low compression on one or more cylinders) are less common causes for a P0174 but can contribute to lean readings if persistent.

SYMPTOMS

• Check Engine Light (MIL) is illuminated.
• Rough idle or stalling, particularly at idle or during acceleration.
• Hesitation, bucking, or reduced power under acceleration.
• Decreased fuel economy.
• O2 sensor readings may alternate between lean and rich if the system is trying to compensate.
• No obvious external leaks; sometimes symptoms are silent except for the MIL.

DIAGNOSTIC STEPS (practical, data-driven approach)

Recommended approach emphasizes live data beyond the bare code. You’ll want an OBD-II scan tool with live data capability and, ideally, a smoke machine for leaks.

• Step 0: Confirm and gather data

  • Confirm the P0174 code and note any freeze-frame data.
  • Record live data: short-term fuel trim (STFT) and long-term fuel trim (LTFT) for bank 1 (and bank 2 if the scanner shows both banks).
  • Note intake air temperature (IAT), MAF sensor reading (grams/sec or pounds/min), MAP sensor reading (if present), RPM, engine coolant temperature (ECT), fuel pressure (if you have a gauge), and O2 sensor readings (upstream and downstream).

• Step 1: Check for obvious air leaks and vacuum integrity

  • Visually inspect hoses, connections, and the intake manifold for signs of wear or disconnection.
  • Perform a smoke test to reveal vacuum leaks around intake, throttle body, and PCV connections.
  • Inspect PCV valve and hose; replace if sticky or clogged.

• Step 2: Inspect the MAF sensor and air path

  • Remove and inspect the MAF sensor for contamination (dust, oil, dirt). Clean with a dedicated MAF cleaner; do not touch the hot wires.
  • Check air filter condition; replace if dirty or restricted.
  • After cleaning or replacement, recheck fuel trim values. A clean MAF that reads normally often reduces elevated trims.

• Step 3: Check fuel delivery

  • If LTFT is consistently high (e.g., +8% to +25% or higher) with low or normal STFT, suspect fuel delivery or air leaks rather than the MAF.
  • Check fuel pressure with a gauge to ensure it’s within the factory specification for your Camry engine (2.5L four-cylinder variants). If you’re unsure, refer to the service manual for exact numbers; low pressure points to fuel pump, filter, or regulator issues.
  • Consider testing for injector performance (listen for a clicking sound with fuel pressure stable; consider a professional injector test/clean if needed).

• Step 4: Inspect the O2 sensors

  • Upstream O2 sensor should switch between rich and lean as the engine runs; if it’s slow to switch or stuck, it could be out of spec and causing improper fueling.
  • If possible, compare upstream O2 sensor data to downstream sensor; persistent lean readings upstream with normal downstream readings point toward fuel or air issues rather than a sensor fault.

• Step 5: Inspect the EGR system

  • A stuck-open EGR valve or restricted EGR passages can cause lean indications or rough operation. If accessible, clean the EGR valve and passages or replace if faulty.

• Step 6: Check for exhaust leaks

  • Look for leaks before the oxygen sensors (manifold or flange leaks). Even small leaks can cause erroneous lean readings.

• Step 7: Rule out misfires

  • If P030x codes (cylinder misfire) appear or a misfire is observed, address ignition or injector issues that can masquerade as lean conditions.

• Step 8: Reset and road-test

  • After any repair or cleaning, clear the codes and drive the vehicle through a typical load, highway, and idle cycle to observe whether LTFT and STFT stabilize within normal ranges (roughly near 0% to small positive/negative values, depending on bushing and engine operating conditions).
  • If LTFT returns to elevated levels after reset, reassess the previously addressed path (vacuum leaks, MAF, fuel delivery, EGR, etc.).

• Data interpretation pointers

  • True lean condition signatures: LTFT persistently positive and significant, with STFT cycling toward the same direction.
  • A cleaning or replacement that reduces LTFT significantly indicates the prior problem was related to that component (e.g., dirty MAF, vacuum leak, or dirty air filter).
  • No persistent fuel trim issue with a target air-fuel ratio generally points toward a temporary sensor fault or a minor air leak that is intermittent.

RELATED CODES

• P0171: System Too Lean (Bank 1) — the more common lean code for a single-bank engine like many Camrys; symptoms and causes are similar to P0174.
• P0300: Random/Multiple Cylinder Misfire Detected — may appear if the lean condition causes misfires or if misfires exacerbate fuel trim behavior.
• P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient — can contribute to lean operation if EGR is blocked or restricted.
• P0420/P0430: Catalyst Efficiency (Bank 1/Bank 2) — usually not primary causes of a lean code, but a persistent lean condition can stress the catalytic converter.

REPAIR OPTIONS AND COSTS (2025 PRICES)

Note: Costs vary by region, shop rates, and exact Camry engine variant. All prices are ballpark ranges for typical Camry models (2018-2024) and assume standard labor rates.

• Vacuum hoses, seals, PCV valve replacement

  • Parts: $10–$60
  • Labor: $70–$180
  • Typical total: $80–$240

• Mass Air Flow (MAF) sensor replacement

  • Parts: $140–$320
  • Labor: $60–$120
  • Typical total: $200–$440
  • Cleaning (not replacement): $20–$60

• Air filter replacement

  • Parts: $10–$40
  • Labor: $0–$20
  • Typical total: $10–$60

• Fuel system (fuel pressure test, pump, filter, regulator)

  • Fuel pressure test kit/parts: $0–$60 (gauge rental or purchase)
  • Fuel pump replacement (in-tank) with regulator: $500–$1,000 parts + $150–$350 labor (varies by engine and access)
  • Fuel filter replacement (if applicable): $60–$150 parts + $50–$100 labor
  • Injector cleaning or replacement: $50–$150 per injector (cleaning typically cheaper)

• Upstream O2 sensor replacement

  • Parts: $120–$300
  • Labor: $80–$150
  • Typical total: $200–$450

• EGR valve cleaning or replacement

  • Cleaning: $60–$180 labor (parts often minimal)
  • Replacement: $300–$800 parts + $150–$250 labor

• Intake manifold gasket or related gasket replacement

  • Parts: $50–$250
  • Labor: $300–$900
  • Typical total: $350–$1,150

• Throttle body cleaning or replacement (if applicable)

  • Cleaning: $60–$120 labor
  • Replacement: $350–$800 parts + $100–$200 labor

• General note:

  • If multiple components are implicated or there is a persistent lean condition, a complete diagnostic and replacement plan may run $500–$1,500+ depending on parts replaced and labor time.

DIY VS PROFESSIONAL

• DIY-friendly tasks (good for beginners to intermediate):
  • Replacing air filter.
  • Cleaning MAF sensor (with dedicated cleaner) and reconnecting wiring carefully.
  • Inspecting for obvious vacuum leaks visually; performing a basic hose and PCV valve check.
  • Checking for trouble codes and clearing codes after basic fixes; retesting with drive cycle.
  • Basic throttle body cleaning (without removing the throttle plate) if accessible and not disassembling critical components.
• DIY tasks that benefit from professional service:
  • Accurate fuel pressure testing and diagnosing fuel delivery issues.
  • Smoke testing for vacuum leaks (requires equipment).
  • Exhaust leak checks and EGR system diagnostics (requires specialized tools and knowledge).
  • Injector testing/cleaning or replacement.
  • O2 sensor diagnostics and replacement (requires correct sensor type and torque specs).
  • Any job involving removal of intake manifolds or gasket replacement due to potential engine damage if done improperly.
• Safety considerations:
  • Working with the fuel system and electrical components carries fire and shock hazards. Use proper PPE, disconnect battery as needed, and ensure the area is well-ventilated.

PREVENTION

• Regular maintenance to minimize lean conditions:
  • Replace air filter at recommended intervals; use high-quality filters.
  • Use clean, quality fuel; avoid ethanol-heavy lower-quality fuels when possible.
  • Schedule periodic MAF sensor cleaning if you notice irregular idle or fuel trim fluctuations.
  • Replace PCV valve and hoses as per maintenance schedule; inspect for cracks or oil leaks.
  • Keep vacuum hoses in good condition and replace cracked or swollen hoses promptly.
  • Ensure proper engine tuning and timely spark plug replacement to avoid misfires that can complicate lean readings.
  • Address exhaust leaks and EGR issues promptly; even small leaks can affect sensor readings and fuel trims.
  • If you have a persistent lean condition, perform a thorough diagnostic rather than repeatedly replacing parts.

Important data caveat

• The dataset you provided does not list P0174 as a complaint for 2018-2024 Toyota Camry, and it shows no recalls for this model in NHTSA. The diagnostic guide above is based on general, widely accepted lean-condition diagnosis practices for Toyota Camry engines in these years. If you have access to vehicle-specific service information or TSBs for your exact VIN, those should take precedence.

If you’d like, I can tailor this guide to your exact Camry variant (engine code, generation, trim) and help you interpret live data logs you’ve captured (STFT/LTFT ranges, MAF readings, O2 sensor curves) to pinpoint whether the issue is vacuum-related, fuel-delivery related, or sensor-related.