P0304 Code: Toyota Camry (2018-2024) - Causes, Symptoms & Fixes

No recalls found in NHTSA database

Note on the data: The supplied NHTSA data for Toyota Camry (2018-2024) includes one owner complaint (P0442) and notes no recalls. There is no NHTSA entry in the provided data for P0304. The guide below focuses on P0304 (Cylinder 4 Misfire Detected) for 2018-2024 Toyota Camry, and uses general automotive knowledge tailored to Camry 4-cylinders. If you are chasing a P0304 diagnosis, treat this as a structured starting point, with vehicle-specific checks depending on your exact Camry configuration.

1. CODE MEANING AND SEVERITY

• Code definition: P0304 = Cylinder 4 misfire detected. The engine control module (ECM) has detected that cylinder 4 is not combusting properly.
• Typical symptoms: rough idle, engine shake, reduced engine power, hesitation or stumble during acceleration, possible temporary fuel cutoff to the misfiring cylinder, and a flashing or solid MIL (check engine light) depending on severity.
• Severity note: A persistent misfire can cause increased emissions, poor drivability, and potential damage to the catalytic converter if unburned fuel passes into the exhaust. If the misfire is severe or occurs under load, seek repair promptly.

2. COMMON CAUSES ON TOYOTA CAMRY

• Ignition system
  • Faulty ignition coil on cylinder 4 (coil-on-plug is common in Camrys). A weak or failing coil often causes a misfire that follows the coil.
  • Worn or fouled spark plug in cylinder 4 (gap incorrect, deposited fuel or oil fouling, degraded plug type).
• Fuel delivery
  • Faulty or dirty fuel injector for cylinder 4 (clog, poor spray pattern, or electrical fault causing injector not to energize).
  • Low or unstable fuel rail pressure affecting one cylinder.
• Air and vacuum
  • Vacuum leak or split hose near cylinder 4 intake path or a leaking intake manifold gasket.
  • Mass air flow (MAF) or intake air leak causing a lean condition that can trigger misfire.
• Mechanical and compression
  • Low compression in cylinder 4 (valve issue, piston ring problem, or gasket problems). This is less common but can cause persistent misfire.
• Sensors and electrical
  • Wiring harness or connector issue to cylinder 4 coil and/or injector (corrosion, loose connector).
  • ECU/PCM intermittent issue (less common; usually accompanied by other codes).
• Other
  • Dirty/contaminated engine oil or coolant mixing into a combustion chamber due to an internal issue (less common; diagnose with compression and leak-down tests).

3. SYMPTOMS (P0304–Cylinder 4 Misfire)

• MIL illuminated, often with P0304 stored in memory or active.
• Rough idle or vibration, especially at idle or during light loads.
• Decreased engine power or hesitation when accelerating.
• Decreased fuel economy and possible increased exhaust emissions.
• In some cases, misfire may only occur under certain conditions (e.g., cold start, acceleration, or high load).

4. DIAGNOSTIC STEPS
   Start with safety and data collection, then perform stepwise testing to isolate cylinder 4 misfire.

A. Confirm the code and current symptoms

• Use a diagnostic scan tool to confirm P0304 and note any freeze-frame data, misfire counters, and live data for cylinder-by-cylinder misfire.
• Check for related codes (P0300, P0301, P0302, P0303, P0305-P0308) which indicate misfires in other cylinders.

B. Inspect obvious wear and components

• Spark plug on cylinder 4: remove and inspect; look for wear, improper gap, oil fouling, or heavy carbon buildup. Replace if needed.
• Ignition coil on cylinder 4: inspect for cracks, heat damage, or corrosion on the connector. Swap test (see below) if feasible.
• Check the coil-on-plug wiring harness and connector for corrosion or loose fit.

C. Perform a swap and isolate

• Coil swap test:
  • Move the ignition coil from cylinder 4 to another cylinder (e.g., cylinder 2) and see if the misfire follows the coil.
  • If the misfire follows the coil to the new cylinder, the coil is faulty.
  • If the misfire remains on cylinder 4, the issue is not the coil; proceed to fuel/air/valve checks.
• Injector test:
  • Swap the injector for cylinder 4 with another cylinder’s injector (if compatible). If the misfire moves with the injector, the injector is likely the problem.
  • If the misfire stays on cylinder 4, focus on the injector’s wiring or the cylinder’s compression.

D. Fuel and air system checks

• Fuel trim and fuel pressure: use the scan tool to view short-term and long-term fuel trims. A persistently lean or rich condition can point to injector or sensor issues.
• Fuel pressure check: confirm rail pressure is within specification for the Camry’s fuel system. A drop in pressure can cause a misfire on one cylinder under load.
• Vacuum/air leaks: inspect vacuum lines and the intake manifold gasket near cylinder 4. Use a spray test (e.g., carb cleaner or propane) around gaskets while the engine runs to detect a change in idle.
• MAF/air intake: ensure the MAF sensor is clean and within spec; ensure intake air path is free of obstruction and there are no vacuum leaks.

E. Mechanical checks

• Compression test / leak-down test on cylinder 4 to verify mechanical condition.
  • If compression is low or leak-down is excessive, there may be valve seating issues, piston ring wear, or a head gasket problem.
• If available, perform a leak-down test to pinpoint the cylinder’s sealing issue.

F. Sensor and ECM considerations

• Inspect relevant wiring to the cylinder 4 coil and injector. Look for damaged insulation, loose pins, or corrosion.
• If all hardware tests are normal, consider a software update or ECM reflash as a last resort per dealer bulletin, but be sure to verify service feasibility and warranty implications.

G. Recheck after repairs

• Clear codes, perform a road test, and watch for reoccurrence of P0304 and any new PCM codes.
• If P0304 returns, revisit compression, injector testing, and valve condition.

5. RELATED CODES

• P0300: Random/Multiple Cylinder Misfire Detected.
• P0301, P0302, P0303, P0305, P0306, P0307, P0308: Misfire codes for cylinders 1–8 respectively.
• P0304 is specific to cylinder 4; misfire in other cylinders may indicate a shared root cause or multiple issues.
• Other codes that can accompany misfire: P0171/P0174 (system too lean or rich), P1110 (MAP sensor range/performance issues in some applications), P0401 (exhaust gas recirculation flow insufficient) and P0402 (EGR flow excessive) depending on the engine and model year.

6. REPAIR OPTIONS AND COSTS (2025 PRICES)
   Prices vary by region, labor rate, and exact Camry engine (4-cylinder vs V6). The following are rough ranges you can expect for a typical 4-cylinder Camry (2018-2024) repair in the U.S. If multiple components are involved, total costs will be higher.

• Spark plug replacement (cylinder 4 only)

  • Parts: $5–$20
  • Labor: 0.3–0.5 hours
  • Typical total: $60–$160
  • Note: Many technicians recommend replacing all four spark plugs at the same time to prevent future misfires across cylinders; if replacing all, multiply by 4 plugs.

• Ignition coil replacement (cylinder 4)

  • Parts: $60–$150
  • Labor: 0.3–0.5 hours
  • Typical total: $120–$250
  • If the misfire is confirmed to follow the coil, this is often the most cost-effective fix.

• Fuel injector for cylinder 4

  • Cleaning (no replacement): $0–$50 (additive cleaners or professional cleaning service)
  • Replacement injector: $120–$350 (parts)
  • Labor: 1–2 hours
  • Typical total: $180–$800
  • Note: If the injector is stuck or severely dirty, replacement is more reliable than cleaning.

• Vacuum leak repair (manifold gasket, hoses, PCV, etc.)

  • Parts: $20–$200 (depending on part)
  • Labor: 2–4 hours
  • Typical total: $200–$900

• Compression test / mechanical repair (valve, piston rings, head gasket)

  • Compression test: $100–$250 (labor and inspection)
  • If mechanical repair required: valve job, gasket replacement, or piston ring work
  • Typical total: highly variable, often $1,000–$4,000+ for substantial repairs

• ECU/PCM software update or replacement

  • Software update: $50–$150 (dealer or independent shop, sometimes included with a diagnostic)
  • PCM replacement: $800–$1,500 (parts + labor), plus programming

• Combined failures (e.g., coil + plug + injector)

  • Expect higher totals; a shop may package these as a single repair if multiple components are found to be faulty.

7. DIY VS PROFESSIONAL

• DIY-friendly options (if you have basic tools and automotive experience)

  • Inspecting and replacing the spark plug on cylinder 4.
  • Testing/swapping ignition coil with another cylinder to verify coil fault.
  • Swapping injector with another cylinder (if compatible) to identify injector fault.
  • Visual inspection of ignition coil wiring and connectors.

• More advanced tasks (recommended for professionals)

  • Accurate fuel pressure testing, leak-down/compression testing, and diagnosing intermittent electrical faults.
  • Injector diagnostic with lab tooling (noid light tests, controlled feed).
  • Vacuum/pressure smoke testing and timing checks (if needed).
  • ECU/software updates or reprogramming.

• Safety and cost considerations

  • If you’re not comfortable working near the fuel system, high-voltage ignition components, or performing compression tests, seek a qualified mechanic.
  • Incorrect diagnosis or improper reinstall torque on spark plugs and coils can lead to further issues.

8. PREVENTION

• Regular maintenance
  • Replace spark plugs at the recommended interval for your Camry engine (roughly every 100,000 miles or as specified by Toyota for your engine variant; if you drive hard or in harsh conditions, earlier replacement may be beneficial).
  • Use OEM-recommended spark plugs and ignition components; ensure torque specifications are followed.
• Air and fuel system care
  • Maintain clean air filters and inspect intake paths to prevent debris from entering cylinders.
  • Use top-tier fuel and consider occasional fuel injector cleaner treatments as per manufacturer recommendations.
• Vacuum and PCV system care
  • Inspect vacuum lines and PCV valve for cracks or clogging; replace as needed to maintain proper air/fuel mixture.
• Electrical system maintenance
  • Keep coil-on-plug connections clean and dry; address any wiring harness damage promptly.
• Driving habits
  • Gentle driving at cold starts initially and gradual throttle application can reduce misfire risk due to cold engine conditions or deposit buildup.
• Timely diagnosis
  • Address misfire codes promptly to prevent potential catalytic converter damage or engine damage from lean/rich misfires.

Summary

• P0304 for the Toyota Camry (2018-2024) indicates a misfire in cylinder 4. While the supplied NHTSA data mentions P0442 and notes no recalls, there is no P0304-specific data in the provided dataset. Use the diagnostic steps above as a structured approach to identify whether the issue is a faulty spark plug, ignition coil, injector, vacuum leak, compression problem, or a combination. Costs shown are approximate 2025 values and can vary by region and shop. If you lack mechanical experience, a professional diagnosis is advised to minimize risk and ensure correct repair.

If you’d like, I can tailor the diagnostic steps to your exact Camry configuration (engine size and model year) and provide a more precise parts list and costs based on your location.