P0302 on 2012-2016 Subaru Impreza: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2012-2016 Subaru Impreza

While P0302 is a generic code, its diagnosis on the 2012-2014 Impreza is unique due to Subaru's recall WTY-84 (NHTSA Campaign 18V772000 🎬 Watch: Understanding the Subaru valve spring recall and repair process.) for valve springs that could fracture and cause misfires. This is a serious mechanical issue that must be ruled out, as the dealer repair involves removing the engine to replace the springs. Additionally, oil leaks from valve cover tube seals are a common boxer engine trait that can foul spark plugs. This can be exacerbated by the excessive oil consumption issue documented in TSB 02-157-14R for some early FB20 engines, which can also lead to fouled plugs and misfires.

Symptoms You May Notice

• Rough idle or shaking, especially when stopped
• Flashing or solid Check Engine Light
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Decrease in fuel economy
• Engine stalling

Most Likely Causes

1. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item with a replacement interval of around 60,000 miles. Leaking valve cover tube seals, common on boxer engines, can also foul the plugs with oil, causing premature failure. Some early FB20 engines also suffered from excessive oil consumption (per TSB 02-157-14R), which can also cause spark plug fouling.
   How to confirm: Remove the spark plug from cylinder 2 and inspect it for wear, heavy carbon deposits, or oil fouling. Compare it to a new plug.
   Typical fix: Replace the spark plug. It is recommended to replace all four spark plugs at the same time for balanced performance. 🎬 See this walkthrough for replacing spark plugs on the FB20 engine.
   Est. part cost: $10-$25 per plug
2. Failed Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are subjected to high heat and can fail over time. The FB20B uses a coil-on-plug design, and failure of a single coil is a very common cause for a single-cylinder misfire.
   How to confirm: Swap the ignition coil from cylinder 2 with another cylinder (e.g., cylinder 4 on the same side). Clear the codes and drive the vehicle. If the code changes to P0304 (Cylinder 4 Misfire), the coil is faulty.
   Typical fix: Replace the failed ignition coil.
   Est. part cost: $50-$100
3. Fractured Valve Spring (2012-2014 models) 🟡 Medium Probability Subaru issued recall WTY-84 (NHTSA #18V772000) for 2012-2014 Imprezas due to valve springs that could fracture, causing misfires, noise, and potential stalling. This is a known manufacturing defect.
   How to confirm: Check your vehicle's VIN on Subaru's recall website or with a dealer to see if the recall applies and if it has been performed. A compression test or leak-down test can also point to a valve sealing issue.
   Typical fix: If the recall is open, a Subaru dealer will perform the repair, which is extensive and involves engine removal, at no cost. Owners on forums have reported dealer service times ranging from a few days to several weeks.
   Est. part cost: $0 (if recall applies)
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: After ruling out ignition issues, you can swap the fuel injector from cylinder 2 with another cylinder. If the misfire code follows the injector, the injector is the problem. This is a more involved diagnostic step.
   Typical fix: Replace the faulty fuel injector. It's often recommended to have all injectors professionally cleaned and tested at the same time.
   Est. part cost: $70-$150

Rare But Worth Checking

• Leaking Valve Cover Gasket / Spark Plug Tube Seals: → Shop Engine Valve Cover While the leak itself doesn't cause the misfire, the oil it allows into the spark plug tube will foul the spark plug and degrade the ignition coil boot, leading to a P0302 code. If you find oil on the spark plug, you must fix the leak.
🎬 Watch: A complete guide to replacing Subaru valve cover gaskets.
• Intake Vacuum Leak: A vacuum leak can introduce unmetered air and cause a lean misfire. While this often triggers a random misfire code (P0300), a leak near the cylinder 2 intake runner could cause an isolated misfire.
• Incorrect Camshaft Position Sensor Clearance: → Shop Engine Camshaft Per TSB 11-130-13R, if P0302 is accompanied by cam sensor codes (P034x, P036x, etc.), the cause may be incorrect air gap on the sensor, not a failed sensor itself. This requires a specific diagnostic procedure to measure and correct the clearance.
• Low Cylinder Compression: Internal engine damage such as worn piston rings, a damaged cylinder head gasket, or a burnt valve can cause a loss of compression, leading to a persistent misfire. This is the least likely cause and should only be investigated after all other possibilities are exhausted.

Diagnosis Steps

1. Read the code using an OBD-II scanner to confirm P0302 and check for any other codes, especially camshaft sensor codes (P034x, etc.).
2. For 2012-2014 models, immediately check your VIN for the WTY-84 valve spring recall on Subaru's website or by calling a dealer. If the recall is open, stop and contact a dealer for the free repair.
3. Locate cylinder 2 (driver's side, rear) and cylinder 4 (driver's side, front).
4. Swap the ignition coil from cylinder 2 with the coil from cylinder 4. Clear the codes, start the engine, and let it run. If the code changes to P0304, the ignition coil is bad and needs to be replaced.
5. If the code remains P0302, move the spark plug from cylinder 2 to cylinder 4. If the code changes to P0304, the spark plug is bad.
6. While the spark plug is out, inspect the spark plug tube for oil. If oil is present, the valve cover gasket and tube seals are leaking and should be replaced.
7. If the misfire remains on cylinder 2 after swapping the coil and plug, the issue is likely a fuel injector or a mechanical problem.
8. Consider swapping the fuel injector between cylinders to see if the misfire follows. This is a more advanced step.
9. If all else fails, or if cam sensor codes are present, investigate mechanical issues. Perform a compression test and a cylinder leak-down test to check for bad valves or piston rings. Consider the possibility of incorrect cam sensor clearance as described in TSB 11-130-13R.

Parts You'll Likely Need

• Ignition Coil (OEM #22433AA642) — A common failure item that directly causes a misfire in a single cylinder. Swapping coils is a primary diagnostic step.
  Trusted brands: Denso, NGK, Diamond Electric
  OEM price range: $75-$100
  Aftermarket price range: $40-$70
• Spark Plug (OEM #22401AA781) — A standard wear-and-tear item. Misfires are the most common symptom of a worn-out or oil-fouled spark plug.
  Trusted brands: NGK (SILZKAR7B11), Denso
  OEM price range: $20-$30
  Aftermarket price range: $10-$20
• Valve Cover Gasket Kit (with Spark Plug Tube Seals) (OEM #13294AA070) — Required if oil is found in the spark plug tubes, as this will ruin new plugs and coils. A common leak point on boxer engines.
  Trusted brands: Fel-Pro, Mahle, Subaru (OEM)
  OEM price range: $40-$60
  Aftermarket price range: $25-$40

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or other cylinders are also affected, a P0300 (Random/Multiple Cylinder Misfire) may appear.
• P0301, P0303, P0304 — Misfire codes for other cylinders. If seen together, it points to a systemic issue like the valve spring recall, a major vacuum leak, or low fuel pressure.
• P0340, P0341, P0365, etc. — Camshaft Position Sensor codes. Per TSB 11-130-13R, these codes appearing with a misfire code suggest a potential mechanical timing or sensor clearance issue rather than a simple ignition fault.
• P0420 — A persistent misfire can dump unburnt fuel into the exhaust, damaging the catalytic converter and eventually triggering a P0420 (Catalyst System Efficiency Below Threshold) code.

Technical Service Bulletins (TSBs) & Recalls

• WTY-84 (NHTSA 18V772000): Recall for potential valve spring fracture on 2012-2014 Impreza models.
• 11-130-13R: Diagnostic procedure for misfire codes appearing with camshaft sensor codes.
• 02-157-14R: Addresses excessive oil consumption on early FB20 engines, which can cause spark plug fouling and misfires.

Platform-Specific Known Issues

• Subaru Recall WTY-84: Affects 2012-2014 Impreza models. Valve springs may fracture, causing misfires. This is a critical check for any P030x code on these years. The repair is extensive and requires engine removal.
• Subaru TSB #11-130-13R: Details a link between misfire codes (P030x) and camshaft position sensor codes (P0340, P0341, etc.), suggesting the cause may be incorrect sensor clearance, not a failed sensor.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 10-14 Ohms (for high-impedance injectors typical in this engine). Failure: A reading significantly outside this range, or 'OL' (Open Loop), indicates a failed injector. All injectors should have similar resistance values.
• Fuel Pressure (at idle) — expected: ~43.5 psi (300 kPa). Failure: Significantly lower pressure can cause lean conditions and misfires, though it would likely affect multiple cylinders.
• Scan Tool Misfire Count (Mode $06 or Live Data) — expected: Zero or very few counts on all cylinders.. Failure: A rapidly increasing count on cylinder 2 confirms an active misfire, even if the CEL is not flashing. This is the most direct way to confirm the misfire location.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $53 (or similar): This is not a hidden 'code' but a data monitor within the OBD-II system that tracks misfire counts for each cylinder per drive cycle. It can show misfires occurring on cylinder 2 before they are frequent enough to set the P0302 trouble code, making it invaluable for diagnosing intermittent issues. (see via An advanced OBD-II scanner or software that can display Mode $06 data. The Subaru Select Monitor (SSM) dealer tool refers to this as the 'Roughness Monitor'.)

Scan Tool Commands That Help

• Subaru Select Monitor (SSM) or equivalent professional scanner: Misfire Count / Roughness Monitor — Use this live data parameter to confirm which cylinder is actively misfiring in real-time. It is especially useful for intermittent misfires that don't consistently trigger a P0302 code, as it will show the raw count for each cylinder.
• Subaru Select Monitor (SSM) or equivalent professional scanner: Fuel Injector Balance Test — This function allows a technician to individually disable one injector at a time to see the effect on engine RPM. If disabling the cylinder 2 injector causes no change in engine roughness, it confirms that the cylinder was not contributing, pointing towards a problem with that injector or cylinder.

Wiring & Ground Locations

• Engine Ground (Intake Manifold) — The main ECU and sensor ground point is typically located on top of the intake manifold.. A poor ground at this location can cause erratic signals for all engine sensors, including the ignition coils and injectors. This can lead to weak spark or incorrect injector timing, causing misfires. It is a critical point to check for corrosion or looseness.
• Chassis Ground (near battery) — The main battery negative cable connects to the chassis near the battery tray.. This is the primary ground for the entire electrical system. While a failure here would likely cause widespread issues, high resistance can lead to intermittent and hard-to-diagnose problems, including misfires.
• Ignition Coil Connector — A 3-pin connector on top of each ignition coil.. The pins for cylinder 2's coil should be tested for 12V power (Key On, Engine Off), a good ground, and a signal pulse from the ECM when cranking. A corroded or damaged connector can mimic a failed coil.

Real Owner Repair Stories

• User on subaruimpreza.org forum (2012 Subaru Impreza) — P0302 misfire code.
  ❌ Tried (didn't work) Replaced spark plugs, Replaced ignition coils
  ✅ What actually fixed it The dealer performed the WTY-84 valve spring recall repair. The fractured spring was the root cause.
• User on NASIOC forum (Subaru with FB20 engine) — P0302, P0304, P0300 codes after basic ignition parts replaced.
  ❌ Tried (didn't work) Spark plugs, Ignition coils
  ✅ What actually fixed it The dealer performed an ECM reflash according to TSB 11-115-12, which updated the logic for misfire detection. This resolved the false codes.
• User on Reddit r/subaru (2013 Subaru Impreza) — Persistent P0302 code.
  ❌ Tried (didn't work) Swapped ignition coil, Swapped spark plug, Swapped fuel injector
  ✅ What actually fixed it A compression test revealed low compression in cylinder 2. The final cause was determined to be a burnt exhaust valve, requiring cylinder head repair.

OEM Part Supersession History

• 22433AA642 → 22433AA643 — Standard revision and update by the manufacturer.

Model Year Variations Within This Range

• 2012-2014: These model years are subject to the WTY-84 valve spring recall. This is the single most important vehicle-specific check for a P0302 code on an early 4th generation Impreza.
• 2015-2016: Following a 2015 model year refresh, the FB20B engine received updates, including redesigned piston rings, to address the oil consumption issues found in earlier 2012-2014 models. As a result, misfires caused by oil-fouled spark plugs are less common on these later models.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Excessive Oil Consumption 🔴 High — Common enough to trigger a class-action lawsuit and TSB 02-157-14R. Affects early FB engines, particularly 2011-2014 models. Consumption over 1 quart per 1200 miles is considered excessive. (Ref: TSB 02-157-14R; Warranty Extension to 8 years/100,000 miles. The fix often involves replacing the entire engine short block.)
• CVT Valve Body Solenoid Failure 🟠 Medium — A common issue where a solenoid in the CVT valve body fails, which can cause hesitation or other shifting abnormalities. It is known to be a hit-or-miss problem, with some failing early and others lasting over 100k miles. (Ref: Subaru extended the CVT warranty to 10 years / 100,000 miles for many vehicles due to this issue.)
• Premature Wheel Bearing Failure 🟠 Medium — Both front and rear wheel bearings are known to fail prematurely, sometimes in as little as 30,000-40,000 miles, causing a roaring or grinding noise that increases with speed.
• Brake Light Switch Malfunction 🟠 Medium — A widespread recall was issued for a faulty brake light switch. Failure can prevent brake lights from illuminating, prevent push-button start vehicles from starting, and block the transmission from being shifted out of Park. (Ref: Recall NHTSA 19V149000)
• Key Stuck in Ignition 🟡 Low — A sensor in the gear shift assembly can fail, preventing the vehicle from detecting that it is in Park. This causes the ignition to lock the key in place. Wiggling the shifter can sometimes temporarily resolve it.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: An ignition coil is a good candidate for a used part, as they are generally robust. Sourcing one from a reputable auto recycler from a lower-mileage donor vehicle can be a cost-effective alternative to a new aftermarket part.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check the plastic housing of the coil for any cracks or signs of heat damage.
• Ensure the rubber boot that seals against the spark plug tube is pliable, not brittle or cracked.
• Inspect the electrical connector for corrosion or broken locking tabs.

Aftermarket brands forum-validated for this vehicle:

• Ignition Coils: Denso, NGK, Diamond Electric (often the OEM supplier)
• Spark Plugs: NGK, Denso
• Gaskets: Fel-Pro, Mahle

Brands owners have reported issues with on this vehicle:

• Unbranded, low-cost ignition coils sold on marketplaces like eBay and Amazon are frequently reported on owner forums to have high rates of out-of-box failure or short service lives.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0304 — Companion misfire code for cylinder 4; used during diagnosis to see if the misfire follows the ignition coil or spark plug when swapped from cylinder 2.
• P0340 — Camshaft position sensor code that often appears alongside misfires on this engine due to incorrect sensor clearance per TSB 11-130-13R.
• P0341 — Camshaft position sensor circuit range/performance code; linked to P030x codes in TSB 11-130-13R regarding sensor air gap issues.
• P0301 — Cylinder 1 misfire; shares the same common causes such as fouled spark plugs from oil consumption or failed ignition coils.
• P0303 — Cylinder 3 misfire; another single-cylinder misfire code that may occur due to the same FB20B-specific issues like valve spring failure or oil fouling.

Frequently Asked Questions