P0304 Code: Nissan Altima (2019-2023) - Causes, Symptoms & Fixes

No recalls found in NHTSA database

No NHTSA complaints are listed for Nissan Altima (2019-2023) related to P0304 in the provided data. As a result, there are no dataset-based statistics to cite for this specific code on this model year range. The diagnostic guide below uses general automotive knowledge for P0304 on a 2019–2023 Nissan Altima, with clearly labeled data limitations.

1. CODE MEANING AND SEVERITY

• Code definition: P0304 means Cylinder 4 Misfire Detected. The engine control unit (ECU) has detected that cylinder 4 is not consistently producing its expected power, or is not firing at all, during regular operation.
• Typical consequences: Rough idle, engine shake, reduced power, and higher fuel consumption. If the misfire is persistent, unburned fuel can pass into the exhaust and potentially damage the catalytic converter and raise emissions.
• Severity (practical): Moderate to potentially high if symptoms are persistent or occur under load or at highway speed. A persistent misfire can lead to catalytic converter damage and reduced drivability.

2. COMMON CAUSES ON NISSAN ALTIMA

• Faulty spark plug on cylinder 4 (wear, fouling, oil fouling, gap out of spec)
• Faulty ignition coil or ignition coil wiring on cylinder 4 (bad coil, cracked boot, damaged connector)
• Faulty or dirty fuel injector on cylinder 4 (sticking, clog, poor spray pattern)
• Vacuum leak or intake manifold gasket issue near cylinder 4 (unmetered air causing lean condition)
• Low compression on cylinder 4 (valve or piston issues, head gasket, ring wear)
• Dirty or contaminated fuel or fuel delivery problem (fuel pump, regulator, or restricted feed)
• Electrical issues (damaged wiring harnesses or connector corrosion to the coil, injector, or PCM)
• Software/engine control issues (rare, but sometimes a recalibration or update is recommended by dealer if indicated by service bulletin)

3. SYMPTOMS

• Rough idle or engine shake at idle
• Power loss or hesitation under acceleration
• Poor throttle response or surging
• Increased exhaust emissions or check engine light on
• Misfire may not be obvious at steady cruise but appears during acceleration or under load
• Short-term or long-term fuel trim shifts (if scanned via a live data tool)

4. DIAGNOSTIC STEPS
   Note: Perform diagnosis with the engine in a safe, well-ventilated area and using appropriate PPE. Start with the simplest, most likely causes and move toward more involved tests.

A. Initial data gathering

• Retrieve DTCs with a scan tool: confirm P0304 and note any related codes (P0300, P0301, P0302, P0303, P0305, P0306, etc.). Check freeze frame data and misfire counter if available.
• Observe live data: spark timing, misfire counter by cylinder, fuel trims (LTFT/STFT), RPM, load, and MAP/MAF behavior.

B. Visual and quick checks

• Inspect spark plug on cylinder 4 for signs of wear, fouling (oil, fuel), or damage. Look for oil on the ground electrode or heavy fouling.
• Inspect ignition coil for cylinder 4: cracks, corrosion at the connector, damaged boot, or obvious damage.
• Inspect wiring and connectors to coil and injector for damage or corrosion.
• Check for vacuum leaks around cylinder 4 area (intake manifold gasket, hoses, PCV lines). Listen for hissing with a mechanic’s stethoscope or use a smoke test if available.

C. Component swap tests (to isolate the faulty component)

• Swap the ignition coil from cylinder 4 with the coil from another cylinder (e.g., cylinder 1 or 3). Clear codes and re-run to see if the misfire follows the coil. If P0304 moves to the other cylinder, the coil is suspect.
• If a dedicated coil is used, swap the spark plug from cylinder 4 with a known good plug from another cylinder and re-check. If misfire follows the plug, the plug is suspect.
• Injector test: listen to injector click on cylinder 4 with a mechanic’s stethoscope. Swap the injector from cylinder 4 with another cylinder if feasible or perform an injector balance test to see if the cylinder’s fuel delivery is the issue.
  D. Fuel system and air delivery checks
• Inspect and test fuel pressure to ensure the cylinder is receiving appropriate fuel. Compare to spec for the Altima engine version (2.5L vs 2.0L turbo).
• Check for lean condition indicators via fuel trim values; persistently high LTFT or large positive/negative trims can indicate a vacuum leak or fuel delivery issue.
• Inspect for dirty air filters and MAF sensor cleanliness; a dirty MAF can cause erroneous airflow readings.
  E. Mechanical checks
• Compression test on cylinder 4 and a comparison to other cylinders. If compression is low, further investigation (valve seating, head gasket, piston rings) is warranted.
• If the engine is a turbo variant (e.g., 2.0L VC-Turbo), ensure there are no turbo-related issues creating abnormal misfiring symptoms (boost leaks, intercooler problems).
  F. ECU/Software consideration
• If no mechanical or ignition/fuel issues are found and other cylinders are not misfiring, consider whether there is a firmware update or calibration notice for the engine management system. This step typically requires dealer-level diagnostics or software updates.

5. RELATED CODES

• P0300: Random/Multiple Cylinder Misfire
• P0301: Cylinder 1 Misfire
• P0302: Cylinder 2 Misfire
• P0303: Cylinder 3 Misfire
• P0305: Cylinder 5 Misfire
• P0306: Cylinder 6 Misfire
• P0307: Cylinder 7 Misfire (if applicable to the engine)
• P0308: Cylinder 8 Misfire (if applicable to the engine)
  Note: For a proper diagnosis, determine whether misfire is isolated to cylinder 4 or if other cylinders show misfire codes as well. This will guide the repair path.

6. REPAIR OPTIONS AND COSTS (2025 PRICES)
   Prices vary by region, shop rate, and whether you choose a dealer or independent shop. The ranges below reflect typical labor and parts in many markets.

• Spark plug replacement (cylinder 4)

  • Parts: $5–$25
  • Labor: 0.5–1.0 hours
  • Estimated total: $100–$250

• Ignition coil replacement (cylinder 4)

  • Parts: $40–$110
  • Labor: 0.3–0.7 hours
  • Estimated total: $100–$180

• Fuel injector testing/cleaning (cylinder 4)

  • Cleaning service: $40–$120
  • Replacement injector (if needed): $120–$350 per injector
  • Labor (injector replacement): 1–2 hours
  • Estimated total (cleaning): $80–$180
  • Estimated total (replacement): $260–$700

• Fuel delivery issues or fuel system service (general)

  • Fuel filter or pressure-related service: $100–$350 including parts and labor

• Vacuum leak repair near cylinder 4

  • Hoses and gaskets: $20–$100
  • Labor: $80–$300 depending on the location and accessibility
  • Estimated total: $100–$400

• PCV valve/valve cover related service

  • Parts: $10–$40
  • Labor: $50–$150
  • Estimated total: $60–$190

• Compression-related repairs (valves, head gasket, rings)

  • Estimated total: $1,500–$4,000+ (varies widely by extent of work required)

• ECU/PCM software updates or re-flash (if indicated)

  • Estimated total: $0–$150 (some dealers may offer this for free; some shops charge a diagnostic fee if no other repairs are made)

Notes on costs:

• Labor rates vary by region and shop. Dealer rates are typically higher than independent shops.
• If multiple cylinders show misfire or if the issue is a common factor (e.g., a common coil pack or injector bank), you may see higher total costs for the replacement of that shared component.
• Always get a written estimate with a clear scope of work and parts.
• If you’re outside warranty and choose aftermarket parts, you can reduce costs but ensure compatibility and quality.

7. DIY VS PROFESSIONAL

• DIY-friendly checks (if you’re comfortable):

  • Inspect the spark plug on cylinder 4 for wear or fouling; compare with other cylinders.
  • Inspect and test the ignition coil for visible damage; swap coil from cylinder 4 with another cylinder to see if misfire moves.
  • Check basic vacuum hoses and PCV lines for obvious cracks or leaks.
  • Perform a basic injector “click test” with a mechanic’s stethoscope (listening for injector operation on cylinder 4).
  • If you have a diagnostic scanner with live data, check misfire counters and fuel trims.

• DIY limitations:

  • Replacing injectors, performing a compression test, or diagnosing deeper engine mechanical issues typically requires tools and expertise best handled by a professional.
  • If the misfire persists after swapping the coil and plug or if compression is poor, seek professional diagnosis.

• When to go professional:

  • If you don’t have a diagnostic scanner, or if you don’t feel confident performing spark plug/coil swaps safely.
  • If compression testing or advanced fuel-air delivery testing is needed.
  • If you suspect engine mechanical issues (low compression, head gasket, valve problems).

8. PREVENTION

• Regular maintenance: follow Nissan’s recommended service intervals for spark plugs and ignition components; many 4-cylinder Altima engines use iridium/platinum plugs, with typical replacement intervals in the 60,000–100,000 mile range, depending on model and usage.
• Use high-quality fuel and keep the fuel system clean with periodic fuel system cleaner only as recommended by the manufacturer.
• Replace air filters timely to prevent unmetered air from affecting fuel trims.
• Address vacuum leaks early; inspect hoses and gaskets during routine service.
• Address any check engine light promptly to avoid catalytic converter damage and to prevent problems from becoming more expensive.

Data limitations

• The provided dataset explicitly states: No NHTSA owner complaints found for this make/model/year/issue combination, and No recalls found in the NHTSA database. Therefore, there are no data-based statistics to quote for this exact code on this vehicle range. The diagnostic guidance above is based on general automotive knowledge for P0304 and typical Altima configurations. If you need the most up-to-date recalls or complaints, please check the official NHTSA database or contact a Nissan dealer for the latest information.