P0302 on 2012-2013 Subaru Impreza: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2012-2013 Subaru IMPREZA

While P0302 is a generic misfire code, the 2012-2013 Impreza with the 2.0L FB20 engine has specific issues to be aware of. The most notable is a factory recall (Subaru recall WTY-84, NHTSA campaign 18V-772) for weak valve springs that could fracture, leading to misfires, engine noise, or stalling. This is a serious issue that required engine removal to perform the repair. Additionally, Subaru issued Technical Service Bulletins (TSBs) like #11-130-13R, which consolidate previous bulletins and detail how misfire codes can be caused by incorrect camshaft position sensor clearances, pointing towards potential valvetrain or timing-related problems beyond a typical spark plug or coil failure.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Flashing or solid Check Engine Light
• Reduced engine power
• Poor fuel economy
• Engine stalling and inability to restart (in severe cases, like a fractured valve spring)

Most Likely Causes

1. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a standard maintenance item. Oil leaking from valve cover gasket tube seals can also foul the plugs, a common issue on boxer engines. The early FB20 engine was also known for potential oil consumption issues which can foul plugs over time.
   How to confirm: Remove the spark plug from cylinder 2 (driver's side, rear). Inspect for wear, damage, or fouling from oil or carbon. A healthy plug should have a light tan color. Look for hairline cracks in the ceramic insulator.
   Typical fix: Replace the spark plug. If oil is present in the spark plug tube, the valve cover gasket and tube seals must be replaced. 🎬 See this walkthrough for replacing your valve cover gaskets and seals.
   Est. part cost: $10-$25 for a single spark plug, $50-$100 for a valve cover gasket set.
2. Failed Ignition Coil 🔴 High Probability
   How to confirm: Swap the ignition coil from cylinder 2 with another cylinder (e.g., cylinder 4, the front cylinder on the driver's side). Clear the codes and run the engine. If the code changes to P0304, the ignition coil is faulty.
   Typical fix: Replace the failed ignition coil. This is a straightforward DIY job with basic tools. 🎬 Watch: How to fix a Subaru misfire with one simple tool.
   Est. part cost: $50-$120
3. Fractured Valve Spring (Recall Issue) 🟡 Medium Probability Subaru issued recall WTY-84 for 2012-2014 Imprezas with the FB20 engine due to valve springs that could fracture, causing misfires, abnormal noise, and potential engine stalling. This recall also affected the 2013 Crosstrek and BRZ.
   How to confirm: Check with a Subaru dealer using your vehicle's VIN to see if the recall work was performed. If not, or if symptoms persist, a compression test and cylinder leak-down test on cylinder 2 can help diagnose internal engine problems.
   Typical fix: If the recall is open, a Subaru dealer will replace the valve springs free of charge. The repair is extensive and requires engine removal. The service can take approximately 15 to 20 hours to complete.
   Est. part cost: $0 if covered by recall; $1000+ if not, due to labor.
4. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: After ruling out ignition issues, a mechanic can perform a fuel injector balance test. An owner on a forum reported fixing a persistent misfire with a quality fuel injector cleaner after plugs and coils didn't work. Swapping the injector with another cylinder is also a valid diagnostic step, similar to the coil swap.
   Typical fix: Clean or replace the fuel injector for cylinder 2. Using a quality fuel system cleaner may resolve minor clogs.
   Est. part cost: $80-$200

Rare But Worth Checking

• Camshaft Position Sensor Fault or Clearance Issue: As noted in Subaru TSB #11-130-13R, misfire codes can appear alongside camshaft position sensor codes (P0340, P0365, etc.). The TSB states the cause can be an incorrect air gap/clearance for the sensor, not necessarily a failed sensor itself. This points to a deeper mechanical timing issue.
• Vacuum Leak: A leak in a vacuum hose or intake manifold gasket can introduce unmetered air, leading to a lean condition and misfires. This would typically cause multiple or random misfire codes (P0300) but can sometimes isolate to one cylinder. A clogged PCV valve can also contribute to these issues.
• Intake Valve Carbon Buildup: While the 2012-2013 Impreza uses a port-injected FB20B, which is less susceptible than later direct-injected versions (FB20D), carbon buildup on intake valves can still occur over high mileage, preventing the valve from seating correctly and causing a misfire. This is more common on cars that are frequently short-tripped.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner. Note any other codes present besides P0302, especially camshaft sensor codes.
2. Locate cylinder 2 (driver's side, rear cylinder).
3. Swap the ignition coil from cylinder 2 with the coil from cylinder 4 (driver's side, front). Clear the codes and drive the vehicle. If the code changes to P0304, the ignition coil is bad and needs replacement.
4. If the code remains P0302, inspect the spark plug in cylinder 2. Check for excessive wear, carbon buildup, or oil fouling. Replace the spark plug if it is worn or damaged.
5. 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.
6. Check your vehicle's VIN with a Subaru dealer or on Subaru's recall website for the WTY-84 valve spring recall. If the recall has not been performed, schedule the service immediately.
7. If ignition components are good and the recall is not applicable or was already performed, perform a compression test and a cylinder leak-down test on cylinder 2 to check for mechanical engine problems like a bad valve or piston ring.
8. If compression is good, the issue may be fuel-related. Try a bottle of high-quality fuel injector cleaner. If that fails, consider swapping the fuel injector from cylinder 2 with another cylinder to see if the misfire follows.

Parts You'll Likely Need

• Ignition Coil (OEM #22433AA642) — A common failure point for misfires. Easy to diagnose by swapping with another cylinder.
  Trusted brands: Denso, NGK, Hitachi, Standard Motor Products (UF-664)
  OEM price range: $90-$150
  Aftermarket price range: $40-$100
• Spark Plug (OEM #22401AA781) — A standard wear item and the first part to check for a single-cylinder misfire.
  Trusted brands: NGK (SILZKAR7B11), Denso
  OEM price range: $15-$25
  Aftermarket price range: $10-$20
• Valve Cover Gasket Kit (with Spark Plug Tube Seals) (OEM #13294AA070) — Leaking spark plug tube seals are a frequent cause of oil fouling on the spark plugs, leading to misfires.
  Trusted brands: Fel-Pro, Beck/Arnley, Subaru OE
  OEM price range: $60-$90
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects other cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0302.
• P0301, P0303, P0304 — These codes indicate misfires in other cylinders. Seeing them together with P0302 points to a systemic problem like a vacuum leak, low fuel pressure, or the valve spring recall issue affecting multiple cylinders.
• P0340, P0341, P0365, P0366 — Subaru TSB #11-130-13R specifically links these camshaft position sensor codes to misfires on this engine. Their presence strongly suggests a valvetrain or timing issue, not a simple ignition fault.

Technical Service Bulletins (TSBs) & Recalls

• 11-130-13R: Provides inspection and repair procedures for misfire DTCs (P0301-P0304) that appear with camshaft position sensor DTCs (P0340, P0365, etc.), pointing to incorrect sensor clearance. This bulletin supersedes several previous, related TSBs.
• 11-125-12: An earlier TSB, now superseded by 11-130-13R, that also linked misfire codes to specific camshaft position sensor codes.
• 02-157-15R: A TSB related to excessive oil consumption on FB engines, which can lead to fouled spark plugs and misfires. It extended the powertrain warranty for this specific issue.

Platform-Specific Known Issues

• Valve Spring Recall (WTY-84): A significant number of 2012-2014 Imprezas were recalled for valve springs that could fracture, causing misfires, rough running, and engine stalling. It is critical to verify if this recall applies to your vehicle and if the service has been completed, as the repair involves engine removal.
• Camshaft Position Sensor Related Misfires: Subaru TSB #11-130-13R details procedures for diagnosing misfire codes that occur along with camshaft position sensor codes. The bulletin suggests the cause is often an incorrect air gap for the sensor, requiring inspection and adjustment, rather than a failed sensor.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: ~1.0 ohm. Failure: A reading significantly higher or lower than the expected value.
• Ignition Coil Secondary Winding Resistance — expected: 10-12 k-ohms. Failure: A reading outside of the specified range indicates a faulty coil.
• Fuel Pressure — expected: Approximately 43 psi (for similar port-injected Subaru models). Failure: Low fuel pressure can cause lean misfires across multiple cylinders, but could isolate to one if an injector is sensitive.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $53 (and others): Mode $06 data tracks misfire counts per cylinder for the current and previous driving cycles, even if the count isn't high enough to set a P0302 code. This is crucial for diagnosing intermittent misfires. (see via An advanced OBD-II scanner capable of displaying Mode $06 data. The Subaru Select Monitor (SSM) calls this 'Roughness Monitor'.)

Scan Tool Commands That Help

• Subaru Select Monitor (SSM) or equivalent: Roughness Monitor / Misfire Count per Cylinder — Use this live data parameter to confirm which cylinder is actively misfiring, especially if the misfire is intermittent and not consistently setting a hard code.
• Subaru Select Monitor (SSM) or equivalent: Freeze Frame Data (FFD) — When a P0302 code is stored, viewing the Freeze Frame Data shows the exact engine conditions (RPM, load, temperature, etc.) when the misfire was first detected, which helps in recreating the fault during diagnosis.

Wiring & Ground Locations

• Main Engine Ground — Bolts to the top starter bolt, connecting the main harness to the engine block/transmission bell housing.. A poor main engine ground can cause erratic behavior in sensors and actuators, including the ignition coils, leading to misfires that can be difficult to trace.
• GE-1 / GE-2 — Top center of the engine, on the intake manifold.. These are primary grounds for engine-mounted components. Corrosion or looseness can affect multiple systems, including ignition.
• ECM (Engine Control Module) — Located behind the dashboard on the right (passenger) side.. All ignition coil and fuel injector signals originate from the ECM. While not a common failure point, knowing its location is critical for advanced electrical diagnosis (e.g., checking for signal at the source).
• Ignition Coil 2 Connector (B21) — On the cylinder 2 ignition coil, driver's side rear of the engine.. This is the direct connection point for testing voltage and signal to the coil. The ECM provides power and a ground signal to this connector to fire the coil.

Real Owner Repair Stories

• MNSubaru forum user 'retreif' (2002 Subaru Impreza (similar ignition system principles)) — Persistent single-cylinder misfire code.
  ❌ Tried (didn't work) Swapping spark plug wires., Inspecting spark plugs.
  ✅ What actually fixed it The fuel injector for the misfiring cylinder was bad and had to be replaced.

OEM Part Supersession History

• 22433AA640, 22433AA641 → 22433AA642 — Standard part revision and improvement by the manufacturer.

Model Year Variations Within This Range

• 2012-2014: When replacing the engine with a JDM (Japanese Domestic Market) unit, the upper oil pan may need to be swapped from the original engine onto the replacement.
• 2012-2013 vs 2017+: The 2012-2013 Impreza uses the port-injected FB20B engine. Starting in 2017, the Impreza switched to the direct-injected FB20D, which has different fuel system components and is more susceptible to intake valve carbon buildup.