P0302 Code: Subaru Impreza (2017-2023) - Causes, Symptoms & Fixes

No recalls found in NHTSA database. No official NHTSA complaints were found for this exact make/model/year/issue combination in the supplied data. This guide combines the code meaning and Subaru-specific considerations with general diagnostic best practices. Data limitations: there are no official complaint counts to gauge prevalence, so the guidance below reflects typical diagnostic approach and common failure items rather than a quantified NHTSA signal for 2017–2023 Subaru Impreza.

CODE MEANING AND SEVERITY

• What P0302 means: P0302 is a diagnostic trouble code that indicates a misfire detected specifically in cylinder 2. The engine control module (ECM) monitors ignition events and combustion; when cylinder 2 misfires, the ECM stores P0302 and typically illuminates the check engine light.
• How severe it can be:
  • Mild/occasional: Intermittent misfire that doesn’t noticeably affect driveability, may have minor fuel economy impact.
  • Moderate: Rough idle, mild power loss, and increased emissions; may trigger the MIL (Malfunction Indicator Light).
  • Severe or persistent: Significant power loss, rough running, potential damage to catalytic converter if unburned fuel enters the exhaust; prolonged misfire can cause overheating of the catalytic converter and further engine issues.
• Implications for 2017–2023 Subaru Impreza: Misfires on a boxer engine can be caused by ignition, fuel, airflow, or mechanical problems. Because cylinder 2 is affected, focus often starts with the ignition coil/plug and the associated wiring, then moves to the fuel injector, vacuum/air leaks, and compression.

COMMON CAUSES ON SUBARU IMPREZA

• Ignition system
  • Faulty ignition coil on cylinder 2 (coil-on-plug design is common on Subaru engines).
  • Worn or fouled spark plug in cylinder 2 (incl. improper gap, oil/fuel fouling, or electrode wear).
  • Damaged or loose coil boot/plug boot connector or ignition coil wiring harness for cylinder 2.
• Fuel system
  • Faulty or sticking fuel injector for cylinder 2 (stuck open/partial clog or coil/injector wiring issue can produce misfire).
  • Low or inconsistent fuel pressure affecting cylinder 2 (fuel pump or pressure regulator issue; fuel quality problems can also contribute).
• Air and vacuum/induction
  • Vacuum leak or cracked intake manifold gasket near cylinder 2 or related vacuum hoses/PCV system.
  • Mass airflow sensor (MAF) orMAP sensor issues causing improper air/fuel mixture that manifests as a cylinder-specific misfire under certain conditions.
• Mechanical/engine health (less common but possible)
  • Low compression in cylinder 2 due to valve, piston, or ring issues, or a head gasket problem affecting that cylinder.
  • Timing or timing-chain tension issues (less common in low-mileage Impreza models with the newer timing systems, but possible if mechanical wear is present).
• Electrical or control/system issues
  • Wiring corrosion or poor connections to cylinder 2’s coil or injector.
  • ECU/PCM communication or software anomalies (rare, but possible; usually accompanied by other codes).

SYMPTOMS

• Check Engine Light (MIL) on with P0302.
• Rough idle on startup or at idle, intermittent or constant misfire feel.
• Hesitation or power loss during acceleration, especially under load.
• Uneven engine RPM, vibration, or shaking felt in the cabin.
• Possible slight drop in fuel economy.
• In some cases, misfire may be more noticeable at certain operating temperatures or speeds.
• If the issue persists, you may also see related codes such as P0300 (random/multiple misfire) or P0352 (ignition coil secondary circuit fault for cylinder 2) depending on the root cause.

DIAGNOSTIC STEPS

Note: Before spending on parts, confirm the misfire with proper testing and avoid replacing components unnecessarily.

• A. Confirm code and data
  • Use a capable OBD-II scanner to confirm P0302 and review live data: misfire counters, cylinder-specific fuel trims, ignition coil primary/secondary data, and misfire history. Check for P0300 (random/multiple misfire) in addition to P0302, which can point to a broader issue.
  • Check freeze-frame data to understand engine load, RPM, and fuel trims when the code was set.
• B. Inspect easily accessible components
  • Remove the ignition coil/coil-on-plug for cylinder 2 and inspect the boot and connector for damage, oil intrusion, or corrosion.
  • Inspect the spark plug in cylinder 2: check electrode wear, gap, and signs of fouling (fuel/oil deposits). Compare with other cylinders.
  • Inspect wiring and connectors to cylinder 2 coil and injector for looseness, cracks, or damaged insulation.
• C. Perform component-level tests
  • Ignition coil test:
    • Swap test: Move the cylinder 2 coil to another cylinder (e.g., cylinder 1) or swap with another coil known-good. If P0302 moves to the new cylinder, coil is likely the culprit; if P0302 remains on cylinder 2 after swap, the coil is likely OK and the issue is elsewhere (plug, injector, or mechanical).
    • Coil resistance check (primary/secondary) against manufacturer specifications if you have the tool.
  • Spark plug test/repair:
    • If cylinder 2 plug is worn or fouled, replace with the proper heat range and torque. Re-gap if applicable (many modern plugs are pre-gapped, but verify).
  • Fuel injector test:
    • Listen for injector operation with a listening stethoscope or DIY noid light test to verify injector pulse to cylinder 2. Check injector resistance against spec.
    • If you suspect the injector is sticking or leaking, consider injector cleaning or replacement.
• D. Fuel and air systems
  • Check fuel pressure to ensure it meets the specification for your engine. Low pressure can cause misfires on one or more cylinders.
  • Perform a vacuum/air leak check around the intake manifold near cylinder 2 (gaskets, hoses, PCV lines). A leak can create a lean condition leading to misfire.
  • Inspect MAF/MAP sensors and related wiring if fuel trims show abnormal values (e.g., consistently high/low short-term or long-term trims).
• E. Mechanical inspection
  • Perform a compression test on cylinder 2 (and nearby cylinders for comparison). If compression is low, proceed with a leak-down test to locate the problem (valve seat, piston, piston ring, or head gasket issues).
• F. Drive-cycle verification
  • After repairs, clear codes and perform a controlled test drive across a range of RPMs and loads to verify that P0302 does not recur and that no new codes appear.
• G. Documentation
  • Keep track of what was tested/replaced and the observed effects. This helps prevent unnecessary replacements and speeds up future diagnostics if the code recurs.

RELATED CODES

• Commonly seen with misfire conditions:
  • P0300 – Random/Multiple Misfire Detected (generic misfire condition not confined to a single cylinder)
  • P0301 – Cylinder 1 misfire
  • P0303 – Cylinder 3 misfire
  • P0304 – Cylinder 4 misfire
• Ignition system related (possible if the misfire is caused by the ignition hardware):
  • P0352 – Ignition coil secondary circuit malfunction (cylinder 2 coil)
  • P0351 – Ignition coil primary/secondary circuit malfunction (cylinder 1 coil)
  • P0353 – Ignition coil primary/secondary circuit malfunction (cylinder 3 coil)
  • P0354 – Ignition coil primary/secondary circuit malfunction (cylinder 4 coil)
• Fuel/air mixture indicators (often accompanying misfire or lean conditions):
  • P0171 – System too lean (Bank 1)
  • P0174 – System too lean (Bank 2) [less common on 4-cylinder but may appear with misfire-related lean conditions]
• If the misfire is related to fuel delivery or air measurement, you may also see intermittent P017x family codes or O2 sensor-related codes as the ECM adjusts fuel trim.

REPAIR OPTIONS AND COSTS (2025 PRICES)

Prices vary by region, shop, and parts choice (OEM vs. aftermarket). The ranges below assume typical independent shops or dealer rates in many areas. All prices are approximate ranges and exclude tax.

• Diagnostics

  • Basic diagnostic fee: $80–$180 (often applied if you bring the car to a shop; some shops waive this with repair).

• Spark plug replacement (cylinder 2)

  • Parts: $6–$20 per plug (OEM or premium replaces may be higher)
  • Labor: 0.5–1.0 hours
  • Estimated total: $90–$260

• Ignition coil replacement (cylinder 2)

  • Parts: $50–$180 for a new coil (coil-on-plug)
  • Labor: 0.2–0.8 hours
  • Estimated total: $100–$380 (for a single coil)

• Spark plug + coil replacement (combo)

  • Estimated total: $150–$380 (depending on OEM vs aftermarket and local labor rates)

• Fuel injector (cylinder 2)

  • Cleaning (non-invasive): $40–$100
  • Replacement injector: $70–$320 per injector
  • Labor: 1.0–3.0 hours (depends on engine layout)
  • Estimated total: $150–$1,000+ (for one injector replacement, including labor)

• Fuel system and pressure test

  • Testing: $100–$200 (may be included in diagnostic or during repair)

• Vacuum/PCV hose and gasket repairs

  • Parts: $5–$100 (depending on hoses or gasket parts)
  • Labor: 0.5–1.5 hours
  • Estimated total: $100–$250

• Mechanical (compression/valve/heads) repair

  • Compression testing and diagnosis: $100–$200 (part of diagnostic)
  • Head gasket/valve repair: typically $1,500–$3,500+ depending on extent and labor rates (rare for 2017–2023 Impreza unless there is a specific mechanical failure)

• ECU/PCM-related anomalies

  • Rare; software reflash or module repair could be $0–$300 if covered under warranty or dealer programs; otherwise, shop time.

Important note: If the misfire is caused by a mechanical issue (low compression, valve seating issue, or head gasket), those repairs are substantially more expensive than ignition or fuel-system fixes. The diagnostic process should determine whether the cylinder 2 misfire is due to ignition, fuel, air, or mechanical concerns before committing to major repairs.

DIY VS PROFESSIONAL

• DIY-friendly tasks (if you have basic tools and mechanical aptitude)
  • Inspecting and replacing a misfiring cylinder’s spark plug: easy and common.
  • Swapping the ignition coil with another cylinder to test whether the misfire follows the coil.
  • Inspecting coil boot and cylinder 2 wiring for obvious damage.
  • Checking for vacuum leaks around the intake manifold with a spray test (careful to avoid engine damage from spray).
• Tasks that typically require a professional
  • Pulling injectors or performing a proper injector balance test if the problem isn’t resolved by ignition components.
  • Verifying fuel pressure with proper gauges and safe procedures.
  • Compression or leak-down tests to confirm mechanical issues.
  • Accessing and replacing head gaskets or performing extensive engine work.
• Safety and care
  • Disconnect the battery when removing/repairing ignition components.
  • When working around the engine, avoid contact with moving parts and hot surfaces.
  • Use OEM or OEM-appropriate parts for reliability, and re-torque fasteners to manufacturer specs.

PREVENTION

• Regular maintenance in line with Subaru’s recommended schedule
  • Replace spark plugs at the manufacturer-recommended interval with the correct heat range and torque; for many Subaru FB-series engines in this era, plugs are designed for longer service life but should be checked and replaced on time.
  • Use quality OEM or high-quality aftermarket ignition coils when replacements are indicated, and inspect coil boots for cracks or moisture.
• Fuel system care
  • Use good-quality fuel and consider occasional injector-safe cleaners if recommended by Subaru or your mechanic, but don’t rely on cleaners to fix mechanical injector issues.
• Air intake and vacuum system
  • Inspect and replace cracked vacuum hoses, especially around the intake manifold and PCV lines; keep the air filter clean to prevent dirty air from affecting combustion.
• Avoiding contamination
  • Address oil leaks or PCV-related issues promptly; oil intrusion into the ignition area can foul plugs and coils.
• Monitoring
  • If you’ve had a misfire on cylinder 2, monitor for recurrence even after a fix; persistent misfires should be re-evaluated to prevent catalytic converter damage and to confirm a lasting repair.

Summary

• P0302 on a 2017–2023 Subaru Impreza indicates a cylinder 2 misfire. In most cases, ignition (coil or plug) or a fuel injector issue is the primary suspect, followed by air leaks or vacuum/PCV problems. If the issue is persistent, perform a thorough diagnostic using coil/plug swapping tests, injector checks, fuel pressure tests, and compression checks to isolate the root cause. No recalls were listed in the provided data, and there were no official complaints found for this exact combination, so the guide focuses on common, practical diagnosis and repair steps. If you’re unsure or the misfire persists after simple fixes, consult a qualified technician to avoid potential damage to the catalytic converter or engine.