P0302 Code: Honda Accord (2018-2023) - Causes, Symptoms & Fixes

P0302 Diagnostic Guide for 2018-2023 Honda Accord (Cylinder 2 Misfire)

Important data note and limitations

• The provided NHTSA data for this exact make/model/year/issue shows no owner complaints and no recalls for P0302. No recalls found in NHTSA database.
• Because there are no complaints or recalls in the provided data, this guide relies on general automotive diagnostic knowledge for ignition/fuel systems and common Honda-specific patterns, plus typical cost ranges for 2025. Real-world results can vary by engine option (1.5L turbo vs 2.0L turbo), trim, maintenance history, and local repair pricing.
• Use this as a diagnostic framework, not a guaranteed fix. Always verify with current scan data and hands-on checks.

1. CODE MEANING AND SEVERITY

• Code: P0302 means a misfire detected in Cylinder 2 by the Powertrain Control Module (PCM) or Engine Control Module (ECM). A misfire is when the air/fuel mixture in a cylinder does not burn properly.
• Severity and impact:
  • Immediate effects: Rough engine operation, reduced power, rough idle, potential stumble on acceleration.
  • Fuel economy and emissions: Increased fuel consumption; higher hydrocarbon emissions; potential catalytic converter heating if misfire is repeated or severe.
  • Long-term risk: Prolonged misfires can damage the catalytic converter and, in some cases, cause engine damage if the misfire is severe and accompanied by low compression or oil/fuel issues.
• Variety of triggers: Misfires can be intermittent or persistent. The DTC can be triggered by a single-cylinder fault that then stops recurring, or by a repeating issue in cylinder 2.

2. COMMON CAUSES ON HONDA ACCORD

• Ignition system
  • Faulty ignition coil on cylinder 2 (coil-on-plug design is common on Hondas; failure is a frequent cause of cylinder-specific misfires).
  • Worn or fouled spark plug in cylinder 2 (gap drift, electrode wear, fouling from oil/fuel).
  • Loose or damaged ignition coil boot/connector to cylinder 2 coil.
• Fuel system
  • Fuel injector for cylinder 2 not delivering proper fuel (stuck open/closed or clogged).
  • Electrical signal issue to injector (wiring/connector problem or injector driver issue).
• Air and vacuum
  • Vacuum leak near the intake runner for cylinder 2 (loose hose, cracked manifold gasket, PCV line).
  • Mass Air Flow (MAF) sensor or air intake restrictions causing lean misfire in cylinder 2 (often accompanied by other codes or sensor data changes).
• Mechanical (less common but possible)
  • Low compression in cylinder 2 due to worn piston rings, valve issue, or leak (head gasket or valve seating problems can cause misfire).
  • Timing or valve train irregularities are rare contributors but can cause misfires in rare cases.
• Miscellaneous
  • Dirty or contaminated fuel, bad fuel injector driver, or PCM/module fault (less common, usually accompanied by additional codes or abnormal data).
• Note for Honda Accord engines: Direct-injected, turbocharged versions (1.5T and 2.0T) can show misfires from injector or valve timing/lean conditions; practical checks often focus on coil/plug and injector health first.

3. SYMPTOMS (P0302 patterns you may notice)

• Rough idle or engine shaking, especially at idle or during light load
• Noticeable loss of power during acceleration or mid-range throttle
• Decreased fuel economy
• Check Engine Light (CEL) or MIL illumination; possible intermittent illumination
• Possible misfire symptoms that come and go with engine temperature (some misfires worsen when cold or hot)
• In some cases, other related misfire codes may appear (P0300 for random/multiple misfires, or P0301/P0303/P0304 if symptoms are cylinder-specific alongside P0302)

4. DIAGNOSTIC STEPS
   Note: Always start with the simplest, most accessible checks and move to more involved tests if the misfire persists.

A. Confirm and collect context

• Use an OBD-II scanner to confirm P0302 and check freeze-frame data (engine rpm, load, engine coolant temp, fuel trims, battery voltage at the time of misfire).
• Check for any pending codes or other cylinder misfire codes (P0300, P0301, P0303, P0304, etc.).

B. Visual inspection

• Spark plug in cylinder 2: remove and inspect for fouling (oil, fuel), wear, or damage; check the plug gap if it’s a non-spark-plug-design engine or if the plug appears older.
• Coil-on-plug/coil boot on cylinder 2: inspect for cracks, oil contamination, corrosion, or damaged boot; ensure connector is clean and firmly seated.
• Wiring and connectors: inspect the coil/injector wiring to cylinder 2 for damaged insulation, loose connectors, or corrosion.
• Vacuum lines and intake runner: look for cracks or loose hoses near cylinder 2; inspect PCV lines and intake manifold gaskets around that runner.

C. Quick correlation tests (swap and observe)

• Swap test (ignition coil): If you have individual coils, swap the cylinder 2 coil with another cylinder’s coil (e.g., cylinder 3). If the misfire follows the coil, the coil is likely bad. If the misfire stays on cylinder 2, the coil itself is likely OK and the issue is elsewhere.
• Plug test: If you have access to a spare known-good spark plug, temporarily swap the spark plug in cylinder 2 and see if the misfire behavior changes. If the misfire follows the plug, replace the plug and recheck.
• Injector signal test (advanced): With a scan tool or oscilloscope, verify injector duty cycle for cylinder 2 when misfire occurs; you can also use a noid light to confirm injector electrical signal. If there’s no signal or the injector presents an abnormal resistance, the injector or its drive circuit may be at fault.

D. Targeted component tests (if initial checks don’t identify the fault)

• Spark plug and coil replacement: If plug or coil are suspect from steps B/C, replace cylinder 2 spark plug and coil (or all four if recommended by you or shop). Re-scan and drive to verify resolution.
• Fuel injector test: If the plug/coil tests are inconclusive and fuel delivery is suspected, test cylinder 2 injector for proper spray pattern and electrical resistance; compare to spec for your engine. Consider professional cleaning or replacement if abnormal.
• Compression test: Perform a dry compression test on cylinder 2 and compare to other cylinders. A significant deviation indicates mechanical issues (valve seating, piston rings, head gasket). If compression is low, further mechanical inspection is needed.
• Vacuum/air leaks: Perform a smoke test or use propane/ carburetor cleaner spray around suspected vacuum leaks to see if engine RPM changes, indicating a leak near cylinder 2.

E. Data-driven decisions

• If misfire is intermittent and occurs with acceleration or cold start, suspect ignition or injector irregularities first.
• If fuel trims are persistently high or low in short/long term trims on cylinder 2, investigate injector, spark, or air/fuel mixture distribution more deeply.

5. RELATED CODES

• P0300: Random/multiple cylinder misfire detected
• P0301: Cylinder 1 misfire
• P0303: Cylinder 3 misfire
• P0304: Cylinder 4 misfire
• Other related diagnostics (use as context):
  • P0171 or P0174: System too lean or rich; may accompany misfire if fuel trim is off
  • P0302 could appear with PCM/engine sensor anomalies in some cases, though usually resolved with the primary cylinder fix

6. REPAIR OPTIONS AND COSTS (2025 PRICES)
   Prices vary by region, labor rates, and whether you use OEM or aftermarket parts. The ranges below assume typical U.S. shop pricing and common engine configurations for 2018-2023 Accord (1.5L and 2.0L turbo options). Costs are approximate and should be verified locally.

A. Spark plug replacement (cylinder 2 or all cylinders)

• Parts: Spark plugs for a 4-cylinder Honda Accord typically range from about $8–$40 per plug (OEM iridium plugs often around $15–$30 each). Replacing all four plugs commonly costs $32–$120 for parts.
• Labor: 0.5–1.5 hours depending on engine variant and accessibility (often 1 hour or more for a 4-cylinder with accessible layout).
• Ballpark total: $150–$300 (parts + labor). If you replace all four plugs, expect the higher end of that range.

B. Ignition coil replacement (cylinder 2 or all cylinders)

• Parts: Coil-on-plug packs typically $40–$120 per coil (OEM or aftermarket). If replacing only cylinder 2, use one coil. If replacing all four, cost increases accordingly.
• Labor: 0.3–1.0 hour per coil, depending on access; coils can be swapped between cylinders to verify cause.
• Ballpark total (single coil on cylinder 2): roughly $120–$260 (parts + labor). For all four coils, $240–$520 or more.

C. Fuel injector replacement or cleaning (cylinder 2)

• Parts: Injectors vary; typical cost to replace a single injector might be $60–$180 for parts. A professional cleaning service may run $100–$250.
• Labor: 1–2 hours or more (can be higher on direct-injected engines due to fuel rail/removal complexity).
• Ballpark total: $180–$550 depending on whether you replace or clean and whether you replace seals or related hardware.

D. Vacuum/PCV line and intake system repair

• Parts: Vacuum hoses and PCV valve typically $5–$60 depending on parts.
• Labor: 0.5–2.0 hours depending on accessibility.
• Ballpark total: $60–$200.

E. Mechanical (compression/valve/head gasket)

• Parts and major repairs: If compression test reveals a mechanical fault (valve issue, bad piston rings, or head gasket), costs can be substantial.
• Ballpark total: Several hundred to several thousand dollars (often $1,000–$4,000+ depending on the severity and whether machine work is required).

F. Miscellaneous

• PCV valve, gasket reseal, or connectors: $10–$200 for parts; $50–$150 for labor typical per item.

Notes on costs:

• The numbers above are general ranges for 2025 and can vary by region, shop rates, and whether OEM or aftermarket parts are used.
• In many cases, mechanics will suggest addressing all four spark plugs and coils when diagnosing a misfire, since worn parts can lead to cross-cylinder issues or intermittent misfires.
• If a compression issue is found, engine-head service or replacement can dramatically change total repair cost.

7. DIY vs PROFESSIONAL

• DIY-friendly steps (if you are mechanically inclined):
  • Read and clear codes with a reliable OBD-II scanner.
  • Inspect cylinder 2 spark plug and coil for obvious damage, fouling, or poor fitment.
  • Swap the cylinder 2 coil with another cylinder to see if the misfire follows the coil.
  • Replace cylinder 2 spark plug if it looks worn or fouled (and test the system after).
  • If you’re comfortable with basic fuel system work, test or swap the cylinder 2 injector or perform a balance test with proper diagnostic tools.
• Professional considerations:
  • If the misfire persists after swapping the plug/coil, testing the injector, and performing a compression test, it’s reasonable to involve a professional to do more advanced tests (injector current tests, fuel trim analysis, live data, and precise compression or leak-down tests).
  • On direct-injected Honda engines, access to certain components can be more challenging; professionals have specialized tools for injector testing, cylinder balance testing, and compression checks.
• Safety and risk:
  • Fuel system work involves fire risk; depressurize the fuel system and follow safety procedures.
  • Always work on a cool engine and disconnect the battery when removing electrical components as required.
  • Use the correct torque specs when reinstalling spark plugs and coils to avoid thread or seal damage.

8. PREVENTION

• Regular maintenance and inspections
  • Replace spark plugs at the manufacturer-recommended interval (and more frequently if the engine shows signs of misfire or rough idle). For many Honda Accord models, spark plugs are long-life, but always follow your owner's manual.
  • Replace ignition coils only when wear or testing indicates failure; inspect coil boots and wiring at each service.
• Fuel system care
  • Use good-quality fuel; consider fuel-system cleaner treatments sparingly and only as directed.
  • If you operate on a lot of short trips, try to accumulate longer drives so the catalytic converter and fuel trims can normalize.
• Air intake and vacuum management
  • Inspect and replace dirty air filters; check for vacuum leaks and fix cracked hoses promptly.
  • Regularly inspect PCV valve and related hoses for wear.
• Engine health checks
  • If you notice ongoing rough idle, power loss, or blinking CEL with P0302, address the issue promptly to avoid catalyst damage or downstream problems.
  • Keep cooling system and oil consumption in check; abnormal oil consumption or coolant loss can contribute to misfire symptoms if the engine’s operating conditions are affected.
• Data-driven prevention
  • If you notice misfires in certain temperature or driving conditions, or if a particular cylinder keeps returning P0302 after plug/coil replacement, consider a more exhaustive diagnostic approach sooner rather than later.

Final notes

• No recalls found in NHTSA database for this exact combination (2018-2023 Honda Accord with P0302) based on the provided data.
• No owner complaints are listed in the provided data for this issue, so there is limited statistical context specific to this model/year for P0302.
• Use the diagnostic steps above as a structured approach. If you lack the tools or have limited experience, start with the low-cost, high-probability fixes (spark plug and ignition coil inspection/replacement) and then move to fuel/injector and mechanical checks as needed. If in doubt, consult a qualified technician to avoid misdiagnosis or unnecessary part replacement.