P0302 on 2012-2018 Mazda 3 Skyactiv: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2012-2018 Mazda 3

The Skyactiv-G is a direct-injection (GDI) engine. Unlike traditional port-injected engines, fuel is sprayed directly into the combustion chamber, not over the back of the intake valves. While this improves efficiency, it means there's no fuel to clean oil deposits from the PCV system off the valves. Over time, these deposits can bake into hard carbon, restricting airflow and causing misfires, an issue specifically addressed by Mazda in TSB #01-012/19. Additionally, early Skyactiv models were subject to a batch of faulty ignition coils from a specific supplier (YUMEBISHI), making coil failure a particularly common cause for this code, as detailed in TSB #01-014/16. Manufacturer service bulletin #01-012-19-3612 further confirms that these Skyactiv engines may experience the Check Engine Light ON with DTC P0302:00 stored in memory due to these combustion instabilities.

Generation note: This range covers the end of the second generation (BL, 2012-2013) and the full third generation (BM/BN, 2014-2018) of the Mazda 3. Both generations offered the Skyactiv-G engine, and the common causes for a P0302 misfire (ignition coils, spark plugs, carbon buildup) are consistent across both.

Symptoms You May Notice

• Check Engine Light is on or flashing
• Rough or shaky idle
• Engine hesitation or stumbling during acceleration
• Noticeable loss of power
• Reduced fuel economy
• Engine stalling

According to TSB #01-010-18-3442b, some vehicles may exhibit an engine misfire specifically during acceleration with the check engine light flashing, even if the DTC is not immediately stored. Furthermore, TSB #01-001-23a notes that customers may complain about poor acceleration and rough idling in conjunction with P0302:00, though this specifically applies to turbo-equipped variants.

Most Likely Causes

1. Failed Ignition Coil 🔴 High Probability → Shop Ignition Coil Mazda issued TSB #01-014/16 for faulty ignition coils from supplier YUMEBISHI on early Skyactiv models. These coils, identified by a 4-digit lot number, were prone to internal failure from temperature changes. The updated, reliable coils are from MITSUBISHI and have a 5-digit lot number.
   How to confirm: Swap the ignition coil from cylinder 2 with another cylinder (e.g., cylinder 3). Clear the codes and drive the vehicle. If the code changes to P0303, the ignition coil is confirmed to be faulty. This is the most common and effective first diagnostic step.
   Typical fix: Replace the failed ignition coil. 🎬 Watch: Step-by-step guide to replacing your ignition coils. It is wise to inspect the lot numbers on the other coils and consider replacing any others from the problematic YUMEBISHI batch (4-digit lot number), especially those made before lot number 6328.
   Est. part cost: $30-$120
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item with a 75,000-mile interval for non-turbo Skyactiv engines. High compression and direct injection can be demanding on plugs, leading to wear or fouling over time.
   How to confirm: After ruling out the ignition coil, remove the spark plug from cylinder 2. Inspect it for a worn electrode, carbon fouling, oil/fuel residue, or a cracked porcelain insulator. A user on a forum noted their persistent misfire was solved by replacing a plug that looked fine but was internally faulty. Swapping the plug with another cylinder can confirm if the misfire code follows.
   Typical fix: Replace the spark plug. It is best practice to replace all four spark plugs at the same time with high-quality Iridium plugs 🎬 See how to properly remove and replace your spark plugs. (e.g., NGK or Denso) to ensure even performance.
   Est. part cost: $15-$25 per plug
3. Carbon Buildup on Intake Valves 🟡 Medium Probability As a direct-injection engine, the Skyactiv-G does not spray fuel over the intake valves, allowing oil vapors from the PCV system to bake on and form carbon deposits that restrict airflow. This issue is common on cars over 60,000-80,000 miles and is addressed in Mazda TSB #01-012/19.
   How to confirm: This is difficult to confirm without a borescope to visually inspect the intake valves. It is often diagnosed by exclusion after ignition and fuel system components have been ruled out. Symptoms are often worse on cold starts.
   Typical fix: The valves need to be cleaned. For mild cases, chemical cleaning (spraying a GDI-specific cleaner 🎬 Watch: How to clean intake valves using a chemical spray. into the intake) may help. For moderate to severe cases, the most effective method is media blasting (e.g., walnut blasting), which requires removing the intake manifold. This is a more involved and costly repair.
   Est. part cost: $20-$40 for chemical cleaner, $400-$800+ for professional media blasting
4. Environmental Factors (Frozen Water) ⚪ Low Probability As detailed in Bulletin #01-007-19-3541, a P0302 code may be caused by frozen water accumulation within the intake system, which can disrupt airflow or sensor readings in cold climates.
   How to confirm: This is most likely if the misfire occurs during or immediately after extremely cold weather.
   Typical fix: Thawing the vehicle in a warm environment and ensuring the intake tract is clear of moisture.
5. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: This is a more advanced diagnostic step. One method is to swap the fuel injector from cylinder 2 with another cylinder to see if the misfire code follows. This requires de-pressurizing the fuel system and removing the fuel rail. A user on a Mazda forum fixed their P0302 by cleaning a visibly clogged injector.
   Typical fix: Replace the faulty fuel injector. It's often recommended to replace the set if they are high mileage. Some owners have had success with professional injector cleaning services.
   Est. part cost: $50-$150 per injector

Rare But Worth Checking

• Low Engine Compression: If all ignition and fuel-related causes are ruled out, a mechanical issue could be the cause. A compression test will reveal if cylinder 2 has significantly lower compression than the others, pointing to a problem with piston rings, cylinder walls, or valves. A subsequent leak-down test can pinpoint the source of the compression loss.
• Vacuum Leak: A vacuum leak near the intake runner for cylinder 2 could lean out the air/fuel mixture and cause a misfire. This would typically be accompanied by other codes like P0300 (random misfire) if the leak is large enough to affect multiple cylinders.
• Wiring Harness or Connector Issue: Damage or corrosion on the wiring or connector for the ignition coil or fuel injector on cylinder 2 can cause an intermittent connection and misfires. This can be a frustrating cause, as one owner on a forum discovered their issue was a brand new, but faulty, ignition coil they were shipped.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm P0302 and check for any other codes.
2. To test the ignition coil, swap the coil from cylinder 2 with the coil from cylinder 3. This requires an 8mm socket. Clear the codes and run the engine. If the scanner now reads P0303, the ignition coil is bad and needs replacement. This is the most crucial first step.
3. If the code remains P0302, inspect the spark plug. Remove the plug from cylinder 2 (requires a 14mm thin-wall spark plug socket) and check for wear, fouling, or damage. You can swap it with the plug from cylinder 3 to see if the misfire follows the plug.
4. If ignition components are good, consider carbon buildup on the intake valves, a known issue with Skyactiv engines, especially over 60,000 miles. This may require professional diagnosis with a borescope or proceeding with an intake valve cleaning procedure.
5. If the misfire persists, the next step is to check the fuel injector. This can be done by listening for a consistent 'clicking' with a mechanic's stethoscope or by swapping injectors, though this is more involved.
6. As a final step for a persistent, isolated misfire, perform an engine compression test to rule out mechanical problems like bad piston rings or valves in cylinder 2.

Parts You'll Likely Need

• Ignition Coil (OEM #PE20-18-100A) — This is the most common failure part for a P0302 code on this vehicle. TSB #01-014/16 specifically calls out faulty coils from supplier YUMEBISHI. The OEM part number PE20-18-100A supersedes earlier versions like PE01-18-100.
  Trusted brands: Mazda (Mitsubishi-produced), NGK, Denso, Bosch
  OEM price range: $80-$120
  Aftermarket price range: $30-$75
• Iridium Spark Plug (OEM #PE5R-18-110 (NGK ILKAR7L11)) — Spark plugs are a routine wear item and the second most likely cause of a single-cylinder misfire after the ignition coil.
  Trusted brands: NGK, Denso
  OEM price range: $25-$40
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0300 — This 'Random Misfire' code can appear with P0302 if the misfire is intermittent or severe enough to confuse the PCM's cylinder-specific detection, or if another issue like a vacuum leak is beginning to affect other cylinders. Bulletin #01-006-18-3429 notes this code often appears alongside cylinder-specific misfires.
• P0301, P0303, P0304 — If other cylinder misfire codes are present, it points towards a systemic problem affecting the whole engine, such as low fuel pressure, a major vacuum leak, or multiple failed ignition coils from the bad batch.
• P0202 — This code for 'Fuel Injector Circuit/Open - Cylinder 2' can appear alongside P0302 when the fuel injector is the root cause. TSB #01-004/17 (which supersedes #01-017/16) notes that these codes are often stored together.

Technical Service Bulletins (TSBs) & Recalls

• Lack of Power/Rough Idle with Misfire DTCs: Addresses P0300-P0304 codes caused by internal failure of YUMEBISHI-supplied ignition coils due to large temperature swings. Advises identifying coils by their 4-digit lot number and replacing with improved MITSUBISHI coils (5-digit lot number).
• Check Engine Light on with Misfire DTCs: Specifically for Skyactiv models, this TSB states that carbon deposited around the intake valves can cause unstable combustion and misfires (P0300-P0304), especially during the warm-up phase.
• Bulletin #01-007-19-3541: Notes that the check engine light may illuminate with DTC P0302 stored in memory due to frozen water within the system.
• Bulletin #01-006-18-3429: Describes instances where P0302 is stored due to environmental factors like frozen water affecting engine performance.
• Rough Engine with Fuel Injector DTCs: → Shop Fuel Injector Notes that on some models, fuel injector circuit/open codes (P0201-P0204) can be stored at the same time as misfire codes (P0301-P0304), pointing to a potential fuel injector or PCM issue.

Platform-Specific Known Issues

• Early Skyactiv engines were fitted with ignition coils from supplier YUMEBISHI that were prone to failure, as documented in TSB #01-014/16. The faulty coils are identified by a 4-digit lot number, while the improved Mitsubishi-made replacements have a 5-digit lot number.
• As a direct-injection engine, carbon buildup on the intake valves is a significant long-term issue. TSB #01-012/19 addresses this problem causing misfires, particularly during engine warm-up. Owners on forums often discuss needing walnut blasting services between 60,000 and 100,000 miles to resolve persistent, otherwise undiagnosable misfires.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.49 - 0.57 Ω at 20°C (68°F). Failure: A reading outside this range indicates a faulty coil.
• Ignition Coil Secondary Winding Resistance — expected: 9.5 - 11.1 kΩ. Failure: A reading outside this range indicates a faulty coil.

Hidden / Shadow Codes Worth Checking

• P0302 Fail-Safe Action: This is not a separate code, but a PCM behavior. When a persistent P0302 is detected, the PCM will command the fuel injector for cylinder 2 to stop firing. This is done to protect the catalytic converter from being damaged by unburnt fuel. (see via This action is noted in Mazda's service manual documentation and can be inferred during diagnosis if there is no injector pulse on cylinder 2 when the code is active.)

Scan Tool Commands That Help

• Mazda IDS (or equivalent professional scanner): Power Balance Test — This function allows a technician to selectively disable individual cylinders one by one. If disabling cylinder 2 causes no change in engine RPM or smoothness, while disabling other cylinders does, it confirms that cylinder 2 is not contributing power, pinpointing the location of the misfire.

Wiring & Ground Locations

• G08 — Located on the left rear of the engine.. Wiring diagrams indicate the ground circuit for all four ignition coils terminates at this point. A loose or corroded connection here could cause intermittent misfires on one or more cylinders, including P0302.
• G02 — Located on the left side of the engine compartment.. This is a primary engine compartment ground point. Poor contact at this location can cause a variety of sensor and actuator issues, including those that might lead to a misfire.
• Ignition Coil Connector — On top of the valve cover, plugged into the cylinder 2 ignition coil.. The connector itself or its wiring can become brittle from heat cycles, causing a poor connection. Check for 12V+ power at the connector with the key on, and verify the integrity of the ground and signal wires back to the PCM.

Real Owner Repair Stories

• Mazda3Club.com user 'KYaniak' (Mazda 3 (generation not specified, but pre-Skyactiv)) — Persistent cylinder 2 misfire (P0302).
  ❌ Tried (didn't work) Replaced #2 spark plug, Swapped ignition coils between cylinders, Moved spark plugs around, Used fuel injector cleaner / Seafoam
  ✅ What actually fixed it The user removed the fuel injectors and found that the injector for cylinder 2 had a large amount of 'crud' on it where it connects to the fuel rail. Cleaning the injector resolved the misfire completely.
• Reddit user 'Nedral69' (Mazdaspeed 6 (different model, but same diagnostic principle)) — Persistent P0302 misfire after extensive part replacement.
  ❌ Tried (didn't work) New spark plugs, Carbon cleaning, Multiple diagnostic tests at a shop
  ✅ What actually fixed it The issue was a brand new ignition coil that was defective out of the box. Replacing the 'new' faulty coil with another new one finally fixed the problem.
• Reddit user 'Danmza10' (Mazda 3 (year/engine not specified)) — P0300 and P0302 codes.
  ❌ Tried (didn't work) Standard troubleshooting (plugs/coils implied)
  ✅ What actually fixed it After taking the car to a dealer, a professional Fuel Injection Cleaning service resolved the issue. The cost was noted to be around $300+.
• Mazdaspeeds.org user 'PlutoMs3' (Mazdaspeed 3) — Rough running, P0304 code that moved to P0302 after swapping coils.
  ❌ Tried (didn't work) Swapped coil packs, Replaced all coil packs and spark plugs, Used fuel injector cleaner
  ✅ What actually fixed it A mobile mechanic with a more advanced scanner found a code for the camshaft positioning sensor that the owner's scanner could not see. The misfire was intermittent and caused by the failing sensor. Replacing the camshaft sensor resolved the misfire codes.

OEM Part Supersession History

• PE01-18-100, PE01-18-100A, P51B-18-100, PE20-18-100 → PE20-18-100A — Revisions to improve reliability and address failures noted in TSB #01-014/16.
• PE01-18-110, PE02-18-110, PE21-18-110, PE5S-18-110, among others. → PE5R-18-110A — Consolidation of part numbers and potential minor updates to materials or design by NGK/Denso for Mazda.
  Heads up: The OEM plug is NGK ILKAR7L11. While many numbers have been used, this is the current recommended replacement.

Model Year Variations Within This Range

• 2012-2013: The first Skyactiv-G engines in the 2nd generation (BL) Mazda 3 used a standard exhaust manifold and a 12.0:1 compression ratio in the US market. The 2014+ 3rd generation (BM/BN) models received the signature 4-2-1 exhaust header which allowed for a higher 13.0:1 compression ratio. While the fundamental cause of a P0302 is the same, the engine's operating characteristics are slightly different.

Diagnostic Flowchart

Real Owner Stories

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

Related OBD-II Codes

• P0300 — Random/Multiple Cylinder Misfire Detected. Often appears with P0302 due to systemic issues like carbon buildup on the intake valves affecting multiple cylinders, as noted in TSB 01-012/19.
• P0303 — Cylinder 3 Misfire Detected. Commonly seen during the diagnostic process if the faulty ignition coil or spark plug from cylinder 2 is swapped to cylinder 3 to confirm the failure.
• P0202 — Cylinder 2 Injector Circuit/Open. TSB 01-004/17 notes that fuel injector circuit codes can be stored at the same time as misfire codes, pointing directly to a fuel injector or PCM issue.
• P0301 — Cylinder 1 Misfire Detected. Shares root causes with P0302, such as the failure-prone YUMEBISHI ignition coil batches identified in TSB 01-014/16.
• P0304 — Cylinder 4 Misfire Detected. Another companion misfire code that can trigger alongside P0302 if the vehicle is suffering from widespread carbon buildup or multiple aging spark plugs.

Frequently Asked Questions