P0304 Code: Honda CR-V (2017-2023) - Causes, Symptoms & Fixes

Below is a comprehensive diagnostic guide for OBD2 code P0304 (-cylinder 4 misfire) as it applies to 2017–2023 Honda CR-V. Notes on data availability from the NHTSA dataset provided: there are No recalls found in NHTSA database for this make/model/year/issue combination, and No owner complaints listed for this issue in the data you supplied. This guide combines that data context with standard automotive diagnostic knowledge to help you diagnose and address P0304 on a CR-V.

CODE MEANING AND SEVERITY

• What the code means: P0304 indicates a misfire detected in cylinder 4. The engine control module (ECM/PCM) has observed an abnormal spark, fuel, or compression event in cylinder 4 sufficient to cause the cylinder not to contribute to engine power.
• Why it matters: Repeated misfires can cause rough running, reduced engine performance, increased exhaust emissions, potential damage to the catalytic converter, and eventually engine overheating or catalyst overheating if left unresolved.
• Severity in a CR-V: A single-cylinder misfire on cylinder 4 can often be addressed relatively quickly if caught early. If the misfire is intermittent or persists, it can lead to rough idle, reduced driveability, and elevated fuel consumption.

COMMON CAUSES ON HONDA CR-V (2017–2023)

Note: This section reflects typical issues seen in CR-Vs with P0304, including the 1.5L turbo engines common in this generation. The data you provided shows no recalls, so these are general diagnostic considerations rather than recall-driven fixes.

• Ignition system
  • Worn or fouled spark plug in cylinder 4 (oil fouling on the plug is common in direct-injection engines).
  • Faulty ignition coil on cylinder 4 or a fault in the secondary wiring/coil boot to cylinder 4.
  • Damaged or corroded coil connector or wiring harness to the cylinder 4 coil.
• Fuel system
  • Clogged or malfunctioning fuel injector on cylinder 4 (sticking injector or poor spray pattern).
  • Low fuel pressure or fluctuating fuel pressure affecting injector performance.
  • Contaminated or degraded fuel that affects combustion stability.
• Air and intake system
  • Vacuum leak near cylinder 4 (intake manifold, PCV hose, gaskets, or hoses).
  • Dirty or restricted air intake components or dirty Mass Air Flow (MAF) sensor affecting air-fuel calibration.
• Engine and compression-related
  • Low compression in cylinder 4 due to worn piston rings, burned valve, or valve seating issues (less common but possible).
  • Timing issues (camshaft/cable timing on pulley systems can affect a cylinder, though less likely as a direct misfire cause for a modern CR-V unless there’s a mechanical fault).
• Miscellaneous electrical/ECM
  • Faulty PCM/ECM misreading (rare; typically confirmed by other codes).
  • Electrical harness fault or a poor ground affecting ignition or injector circuits.
• Real-world CR-V notes
  • On turbo 1.5L engines, carbon buildup around intake valves and injector-related deposits can contribute to misfire symptoms, especially with direct-injection designs. This can elevate cylinder 4 misfire risk if the injector or surrounding valves are affected.
  • Commonly misfires in one cylinder (like 4) move when you swap components (e.g., swap coil from 4 to another cylinder and see if the misfire follows the coil).

SYMPTOMS OF P0304 ON A CR-V

• Check Engine Light (CEL) or MIL on.
• Rough or unstable idle, especially at stoplights or when warming up the engine.
• Noticeable loss of power or hesitation under acceleration.
• Increased fuel consumption or poor drivability.
• Possible sulfur/ rotten-egg exhaust smell if unburned fuel passes through the exhaust.
• OCCASIONAL misfire pattern: sometimes the MIL returns after a restart if the issue is intermittent.

DIAGNOSTIC STEPS (practical, step-by-step)

Safety first: Park safely, let the engine cool if recently driven hot, and ensure you have proper tools and ventilation for testing.

Step 1 — Read codes and freeze frame

• Retrieve all stored DTCs with a scan tool. Ensure P0304 is current or history.
• Check for related codes: P0300 (random/multiple misfire) or P0301, P0302, P0303, P0305, P0306 (misfire on other cylinders). Check for fuel trim (short-term and long-term), misfire counters, and MAP/MAF sensor readings.

Step 2 — Visual inspection

• Inspect spark plug in cylinder 4: look for wear, heat color, fouling (oil/fuel), gaps, or damage.
• Inspect ignition coil and coil wiring to cylinder 4: cracked boot, burnt smell, corrosion, loose connectors.
• Inspect cylinder 4 injector and wiring harness for visible damage, corrosion, or loose connections.
• Check for vacuum leaks around the intake manifold, PCV hoses, and related gaskets near cylinder 4.
• Check air intake hose and air filter condition.

Step 3 — Basic functional tests

• Spark test: Remove the spark plug boot and test for a strong spark (use a proper spark tester or plug/socket method). If there’s no spark on cylinder 4, focus on coil and ignition wiring.
• Coil swap test (diagnostic trick):
  • Move the coil from cylinder 4 to another cylinder (e.g., cylinder 2) and move the ignition coil from that cylinder to cylinder 4.
  • Clear codes and run the engine. If the misfire follows the coil (now on cylinder 2), the coil is faulty; if the misfire remains on cylinder 4, the issue is more likely injector, compression, or wiring.
• Fuel delivery check:
  • Inspect fuel pressure with a suitable gauge at the rail. Compare to spec for the CR-V 1.5L turbo (per service manual). Inconsistent pressure can cause misfires.
  • For direct-injection engines, consider injector resistance check and listening for injector operation (tap test or scope-based “pulse” test). A sticking injector can cause P0304.
• Fuel trim and data check:
  • While idling, observe short-term and long-term fuel trims. A large positive trim on cylinder 4’s bank suggests a lean condition (air leak, injector issue) while a negative trim suggests a rich condition (fuel delivery issues, injector stuck closed, or excessive fueling due to another cylinder misfire).
    Step 4 — More thorough checks if needed
• Compression test: Check static compression in all cylinders, comparing cylinder 4 to the others. Significantly low compression on cylinder 4 indicates mechanical issues (piston, rings, valve, head gasket).
• Leak-down test if compression test is inconclusive.
• Smoke test for vacuum leaks to identify small leaks around intake manifold and vacuum lines.
• Inspect EGR valve operation and PCV system for stick/malfunctions.
  Step 5 — Decision point
• If a swap test clearly identifies the coil as the culprit, replace the coil (and, if needed, the coil boot/wiring harness) and re-test.
• If the plug is fouled or worn, replace spark plugs (and consider correcting injector deposits or carbon buildup if observed).
• If fuel delivery is suspect, service or replace the injector(s) or diagnose fuel pump/fuel delivery issues.
• If compression is low, plan mechanical repair (valve, piston, head, or gasket work) as indicated.
  Note: For a modern CR-V with direct injection and a 1.5L turbo engine, carbon buildup and injector issues can be a common misfire source; a professional diagnosis is often warranted if you encounter persistent misfires after basic ignition components are addressed.

RELATED CODES

• Primary related misfire codes:
  • P0300: Random/Multiple Cylinder Misfire Detected
  • P0301: Cylinder 1 Misfire Detected
  • P0302: Cylinder 2 Misfire Detected
  • P0303: Cylinder 3 Misfire Detected
  • P0305: Cylinder 5 Misfire Detected
  • P0306: Cylinder 6 Misfire Detected
• Emission and sensor codes that may appear alongside misfire:
  • P0171 or P0174: System too lean (bank 1 or 2)
  • P0101-P0104: MAF sensor range or performance
  • P0128 or P2187/P2189: Thermostat or temperature-related issues affecting fuel trim
  • P1299, P030x with P0300: often a general misfire pattern or a secondary issue causing misfire
    Note: The presence of additional codes can help narrow down whether the problem is ignition, fuel, air, or mechanical.

REPAIR OPTIONS AND COSTS (2025 PRICING RANGE)

Prices vary by region, shop, OEM vs aftermarket parts, and whether diagnostics require specialized tools. The ranges below assume typical U.S. labor rates around 100–150 per hour and standard parts quality. These are ballpark figures to help you plan; obtain quotes from multiple shops for accuracy.

A. Quick/low-cost fixes (DIY-friendly or basic shop work)

• Spark plug replacement for cylinder 4 (plus inspecting others)
  • Parts: 4 plugs (OEM or equivalent) around $10–$40 per plug depending on type (iridium or platinum)
  • Labor: 0.5–1.0 hour
  • Estimated total: $120–$250
• Ignition coil replacement for cylinder 4 (if coil suspected)
  • Parts: $40–$120 for the coil
  • Labor: 0.3–0.8 hour
  • Estimated total: $90–$230
• Fuel system cleaner (temporary measure, not a fix for a faulty injector)
  • Parts: $5–$15
  • Labor: minimal
  • Estimated total: $5–$20
    B. Moderate fixes (diagnostics performed, then component replacement)
• Ignition coil(s) and spark plug(s) replacement (if both required)
  • Parts: $60–$180 for plugs and $40–$120 for coil
  • Labor: 0.8–1.5 hours
  • Estimated total: $200–$450
• Fuel injector service or replacement (cylinder 4)
  • Cleaning/injector service: $100–$250 (parts typically included if cleaning a single injector)
  • Injector replacement (one injector): $150–$350 part, $60–$150 labor (per injector)
  • Total per injector: $210–$500
• Fuel pressure test and verification
  • Tools/diagnostics: often included in shop rate
  • Estimated total: $60–$120
    C. More involved diagnostics/repairs (possible mechanical issues or multiple system failures)
• Vacuum/PCV hose replacement and related gasket/seal repairs
  • Parts: $20–$100
  • Labor: 0.5–1.0 hour
  • Estimated total: $120–$250
• Compression test and potential mechanical repairs
  • Compression test: $60–$120
  • If low compression requires mechanical work (valve, piston, head gasket)
    • Estimated total: $1,000–$3,000+ depending on extent
• Carbon buildup valve/valve cleaning (rare in some direct-injection engines without a mechanical issue)
  • Parts: $100–$350
  • Labor: 2.0–6.0 hours (specialized process in some shops)
  • Estimated total: $500–$2,000
    D. Worst-case scenario (engine repair)
• Cylinder head/removal, valve work, or major internal engine repair
  • Estimated total: $2,000–$6,000+ (varies widely by extent and shop)
    Notes
• Always confirm parts quality (OEM vs aftermarket) and check for any applicable warranties.
• If you suspect an intermittent misfire source, seek a diagnostic session that documents the problem with a scan tool and freeze-frame data before replacing components.
• For 2017–2023 CR-Vs with 1.5L turbo engines, many shops recommend a cautious approach: address ignition (plugs/coils) and injector issues first, then verify fuel and compression, to avoid unnecessary major repairs.

DIY VS PROFESSIONAL

• DIY viability:
  • Spark plug replacement on cylinder 4 is generally a DIY-friendly task if you’re comfortable with basic engine work.
  • Coil swapping and basic wiring inspection are also within reach for many DIYers with the right tools.
  • Important cautions: The 1.5L turbo’s direct injection and turbo accessories involve high-pressure fuel systems and electronics. If you’re not comfortable diagnosing fuel pressure, injector testing, or compression testing, or if you lack proper safety equipment, consider professional service.
• When to go professional:
  • If the misfire persists after replacing plugs and coils, or if fuel delivery or compression tests indicate mechanical issues.
  • If you encounter diagnostic data that you don’t know how to interpret (fuel trims, misfire counters, live data at elevated engine load, etc.).
  • If you don’t have the correct tools for high-pressure fuel system testing or for valve/valve-seat cleaning.
• Warranty and safety considerations:
  • If your CR-V is under warranty, consult a dealer for coverage decisions.
  • Working on high-pressure fuel components or attempting to service the turbocharged system should be done with caution and appropriate safety practices.

PREVENTION

• Routine maintenance to reduce misfire risk:
  • Replace spark plugs at Honda-recommended intervals with the correct heat range and type for the 1.5L turbo engine. Using the right plugs helps minimize premature fouling.
  • Replace ignition coils as needed if the manufacturer or a technician identifies coil degradation on specific cylinders.
  • Schedule regular fuel system maintenance: use high-quality fuel with detergent additives, and avoid consistently running low on fuel, which can cause lean conditions and injector varnish.
  • Keep air intake components clean: replace air filters as required; inspect MAF sensor and clean if necessary (use appropriate cleaner that won’t damage sensor elements).
  • Practice good engine combustion health: monitor oil consumption, avoid excessive oil burning which can foul spark plugs; address any oil leaks promptly.
• Specific to the 1.5L turbo CR-V:
  • Be mindful of carbon buildup due to direct injection; if you notice frequent misfires or reduced performance without a clear ignition issue, discuss with a technician whether injector cleaning or valve cleaning is warranted in your mileage range.
  • Address vacuum leaks early; even small leaks can trigger misfire-related symptoms.

Important data limitations

• The data you provided shows No recalls found in NHTSA database and No owner complaints listed for this issue, which means there are no official recalls to reference for this exact combination (P0304 on 2017–2023 CR-V) in the supplied data. This guide uses general automotive knowledge and common misfire troubleshooting practices for the CR-V family in this model year range. If you have access to service bulletins (TSBs) or updated OEM documentation outside the NHTSA dataset, those sources may provide model-specific guidance or requirements not captured here.
• Because P0304 can stem from multiple root causes, a systematic diagnostic approach is essential. If in doubt, consult a qualified technician who can perform hands-on testing and confirm the exact cause before replacing parts.

Final recommendation

• If you’re experiencing symptoms of a cylinder 4 misfire in a 2017–2023 Honda CR-V, start with a careful inspection of spark plug 4 and its coil, then proceed to injector and fuel system checks if the misfire persists. Use a swap test to determine whether the coil or injector is at fault, and verify fuel pressure and engine compression as needed. Given the turbocharged 1.5L engine design and potential for injector/valve deposits, a methodical approach often yields the best results. If the diagnosis exceeds your comfort level or tool availability, seek professional assistance to avoid causing further engine or emissions system damage.

If you want, I can tailor a checklist you can bring to a shop or help you interpret live data from your OBD2 scanner to guide the diagnostic steps for your specific mileage and symptoms.