P0302 Code: Toyota Corolla (2020-2024) - Causes, Symptoms & Fixes

Note on data

• The provided NHTSA data for 2020-2024 Toyota Corolla includes one owner complaint (P0401, electrical/EGR related) and explicitly says there are no recalls found in the NHTSA database.
• There is no official P0302 entry in the supplied data. This guide therefore uses general, widely accepted diagnostic and repair practices for P0302 on a 2020-2024 Corolla, with price estimates valid for 2025. Actual symptoms, tests, and costs can vary by vehicle condition and regional labor rates.

1. CODE MEANING AND SEVERITY

• What it is: P0302 is a Diagnostic Trouble Code indicating a misfire detected specifically in cylinder 2. The engine control module (ECM/PCM) detects that the air/fuel combustion in cylinder 2 did not occur as expected.
• Severity: Moderate to high. A persistent misfire can cause rough running, loss of power, and potential damage to the catalytic converter due to unburned fuel entering the exhaust. Repeated misfires can overheat the catalyst and cause long-term reliability concerns. If the misfire is intermittent, it can be harder to diagnose.
• Typical symptoms: MIL (check engine light) on, rough idle, engine stumble or hesitation, reduced power/acceleration, increased exhaust smell of unburned fuel, occasional engine vibration at idle or during acceleration.

2. COMMON CAUSES ON TOYOTA COROLLA
   Note: This section reflects general, model-relevant causes for cylinder 2 misfire and is not drawn from a P0302-specific NHTSA entry in the provided data.

• Spark plug issue on cylinder 2: worn, fouled, or gaps out of spec.
• Ignition coil failure for cylinder 2: faulty coil-on-plug component or bad primary/secondary winding.
• Cylinder 2 fuel injector problem: stuck open/closed, clogging, or wiring/injector driver issue.
• Wiring/connectors to the coil or injector: damaged insulation, corrosion, or loose connectors.
• Vacuum/air intake issue near cylinder 2: vacuum leak, intake manifold gasket leak, PCV routing affecting cylinder 2.
• Low compression on cylinder 2: valve problems, piston ring wear, piston/ring seating issues, or head gasket problem (less common but possible).
• Battery, alternator, or PCM grounding issues that cause intermittent misfire signals.
• Sensor-driven misfire: incorrect air/fuel calculations due to MAP/MAF, oxygen sensor, or crank/cam sensor timing issues can manifest as a misfire on one cylinder, though the primary cause is still combustion/ignition or fuel delivery on that cylinder.

3. SYMPTOMS

• Primary: Cylinder 2 misfire indicated by P0302 on scan tool or in the ECU’s memory.
• Driving symptoms: rough idle, stumble during light or moderate load, reduced power under acceleration, noticeable engine vibration.
• Emissions/drive-ability: MIL illuminated; potential catalytic converter heat/efficiency concerns if misfire persists.
• Ancillary signs: increased fuel consumption, possible slight smell of fuel from exhaust if combustion is incomplete.

4. DIAGNOSTIC STEPS
   Note: Use a scan tool to confirm P0302 and check any related codes (P0300, P0301, P0303, P0304) and the misfire history. Collect freeze-frame data and check live data for cylinder-specific misfire events.

Step-by-step plan:

• Initial verification

  • Confirm P0302 is current and note any related codes (P0300 etc.).
  • Look at misfire counters and freeze-frame data. See if misfire is persistent or intermittent.
  • Note engine condition (cold vs. hot start, RPM behavior, load, cruising).

• Visual and basic component inspection

  • Inspect spark plug on cylinder 2: condition (worn electrodes, fouling, oil/fuel deposition), electrode gap, and proper seating.
  • Inspect ignition coil for cylinder 2: visible damage, cracks, or arcing; ensure coil connector is clean and seated.
  • Inspect cylinder 2 fuel injector: note any signs of leakage; confirm electrical connector is secure.
  • Check for obvious vacuum leaks near cylinder 2 (vacuum lines, PCV hose, intake manifold gasket area).
  • Check for oil/fuel ingress around spark plug or coil area.

• Quick functional tests (swap-based or testing signals)

  • Spark plug test: if plug is old or fouled, replace with a known-good plug. If new plug resolves misfire, the old plug was culprit.
  • Coil swap test (if you have coil-on-plug arrangement):
    • Swap the coil from cylinder 2 with another cylinder (e.g., cylinder 4) and re-scan after a road test.
    • If the misfire follows the coil (i.e., P0302 moves to P0304 or whichever cylinder you swapped into), the coil is faulty.
    • If the misfire remains on cylinder 2 after swapping, the coil is likely not the root cause.
  • Fuel injector test (if equipped with individual injectors):
    • Listen for injector click on cylinder 2 with a mechanic’s stethoscope; absence or irregularity can indicate a faulty injector.
    • Resistance check: measure injector coil resistance with a multimeter and compare to spec.
    • Use a noid light to verify PCM is firing the injector for cylinder 2; if the signal is present but injector is not delivering fuel, the injector may be clogged or stuck.
  • Live data check:
    • Compare cylinder-specific fuel trim (short-term and long-term) to see if cylinder 2 is running unusually lean or rich.
    • Check MAF/MAF sensor, MAP sensor, and oxygen sensor readings for abnormalities that could contribute to a misfire (e.g., lean condition).
  • Compression test:
    • Perform a compression check on cylinder 2 and compare to the other cylinders. Low compression in cylinder 2 points to mechanical issues (valve, head gasket, rings).
  • Ignition/coil wiring inspection:
    • Check continuity and resistance of the wiring harness to the coil and injector. Look for damaged insulation, corrosion, or loose connectors.
  • If the misfire remains unexplained after the above:
    • Consider a professional diagnostic service to perform advanced tests or an injector balance test.

• When to stop testing and seek professional help

  • If compression is low in cylinder 2 or if you find a mechanical issue (valve seating, etc.).
  • If fuel system tests indicate injector problems that you cannot safely repair.
  • If wiring harness or PCM concerns arise or you are not comfortable performing high-voltage/engine electrical diagnostics.

5. RELATED CODES

• P0300: Random/Multiple cylinder misfire all at once (useful context if misfire is not limited to cylinder 2).
• P0352 (and other P035x codes): Ignition coil secondary circuit issues for the corresponding cylinder; may appear if coil wiring or coil driver fault is suspected.
• P0325 etc. (knock sensor or related if misfire is tied to sensor issues). Note that these codes are not specific to the misfire condition but can accompany misfire if sensors misread the engine load.
• If a coil or injector is swapped and P0302 moves to another cylinder, it supports a component-specific fault (coil or injector).

6. REPAIR OPTIONS AND COSTS (2025 PRICES)
   Prices vary by region, shop, and the exact Corolla trim. The ranges below are general estimates for typical 2020-2024 Corolla with 1.8L engine (non-hybrid) and coil-on-plug setups.

• Spark plug replacement (cylinder 2 only or as part of a set)

  • Parts: $6–$25 per plug (depending on OEM vs aftermarket, iridium vs platinum, heat range)
  • Labor: $40–$120
  • Total typical range: $80–$200
  • Notes: If replacing a full set of plugs, cost will scale with number of cylinders.

• Ignition coil replacement (cylinder 2 coil, coil-on-plug)

  • Parts: $60–$180
  • Labor: $60–$140
  • Total typical range: $120–$320
  • Notes: If the coil is wired to a common module or if the coil is part of a multi-coil pack, price can be higher.

• Fuel injector service (cylinder 2)

  • Cleaning service (professional or hardware-based cleaning): $100–$250
  • Injector replacement (cylinder 2): $180–$350 parts + $60–$180 labor
  • Total typical range: $260–$600 (depending on whether cleaning suffices or replacement is needed)
  • Notes: Direct injection systems can sometimes require cleaning or replacement; in some cases, multiple injectors are replaced as a preventive measure.

• Vacuum leak or manifold gasket repairs

  • Parts: $20–$200
  • Labor: $150–$500
  • Total typical range: $170–$700
  • Notes: Severity depends on leak location and whether port/plenum components are involved.

• Compression-related repairs (valve job, head gasket, piston rings)

  • Parts: widely variable; head gasket kits or full engine work
  • Labor: $800–$2,500 for gasket/seal repairs; engine machining may push higher
  • Total typical range: $1,500–$4,000 (or more in severe cases)
  • Notes: This is a last-resort scenario if compression testing shows persistent low compression in cylinder 2.

• Additional costs

  • Diagnostic fee: $80–$150 (often credited toward repair if you proceed with the shop’s recommended fix)
  • Miscellaneous fluids or gaskets: $10–$100

7. DIY vs PROFESSIONAL

• DIY-friendly tasks (if you have basic hand tools and some mechanical competence)

  • Spark plug replacement: straightforward; requires a spark plug socket, extension, torque wrench, and anti-seize compound lightly (not always required for modern iridium plugs).
  • Coil swap test: simple to perform; requires no special tools beyond basic hand tools.
  • Basic injector testing (noid light, resistance check) can be done with moderate electrical troubleshooting experience.
  • Cautions: Direct-injection engines can have coil-on-plug architectures and sensitive timing; avoid mixing up firing order; ensure the engine is cool and the battery is disconnected for certain electrical tests.

• Professional tasks

  • Persistent misfire after plug/coil replacement
  • Suspected injector clogging that requires ultrasonic cleaning or replacement
  • Low compression on cylinder 2 or suspected valve/head gasket issue
  • Vacuum/PCV area with difficult-to-access leaks
  • Complex wiring harness diagnostics or PCM-related fault codes

• Safety and warranty considerations

  • If your Corolla is under warranty, some repairs may be covered (e.g., defective ignition coil assemblies or injectors if diagnosed as a factory defect).
  • When dealing with high-pressure fuel lines or fuel injectors, professional service is advised for safety and accuracy.

8. PREVENTION

• Regular maintenance

  • Replace spark plugs at the manufacturer-recommended interval with the correct heat range and type for your engine.
  • Use quality fuel and avoid known poor-quality fuels that can leave deposits on injectors or plugs.
  • Follow Toyota-recommended maintenance for ignition components; the 1.8L engine in the Corolla benefits from keeping ignition components in good shape.

• Fuel system care

  • Occasional use of a reputable fuel injector cleaner can help keep direct-injection systems cleaner if recommended by your shop.
  • If you notice rough idle or misfires, address fuel delivery issues early before they cause catalytic converter damage.

• Electrical and harness care

  • Keep connectors clean and dry; ensure battery and charging system are healthy to avoid intermittent ECU miscommunications.
  • Inspect ignition coil and injector connectors for corrosion or looseness during routine maintenance.

• Driving habit

  • Regular highway driving can help keep injectors and combustion chamber deposits in check; avoid excessive short trips that promote carbon buildup.

Data limitations and caution

• The provided data set does not include a P0302 example or related P0302 recalls/TSBs for 2020-2024 Corolla. No recalls were found in the dataset.
• The diagnostic steps above are grounded in general automotive knowledge and typical 4-cylinder, spark-ignition, indirect/direct-injection architectures, and are applicable to the Corolla’s likely 1.8L engine in that model year range. Always verify with a trained technician if you encounter unusual symptoms or if the vehicle has other concurrent issues.

If you’d like, I can tailor this guide to your specific Corolla trim (fuel type, engine variant, and whether it’s hybrid or non-hybrid) and provide a more precise parts list and a step-by-step DIY checklist based on your available tools.