P0302 on 2014-2017 Mazda MAZDA6: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2014-2017 Mazda MAZDA6

While ignition components are the usual suspects, the 2014-2017 Mazda6 with the SkyActiv-G engine has specific issues documented by Mazda. Several Technical Service Bulletins (TSBs) point to unique causes for misfires. TSB 01-014/16 specifically identifies a batch of faulty ignition coils from the supplier YUMEBISHI that are prone to failure. In cold climates, multiple TSBs describe how frozen water in the intake or exhaust system can cause a restriction and trigger misfire codes. Additionally, as a direct-injection engine, the SkyActiv-G can be prone to carbon buildup on intake valves over time, which can restrict airflow and lead to misfires, though this is more common at higher mileage.

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 shaky idle
• Hesitation or stumbling during acceleration
• Flashing or solid Check Engine Light
• Reduced engine power
• Poor fuel economy
• A smell of raw fuel from the exhaust
• Difficulty starting the engine

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability Mazda issued TSB 01-014/16 for 2014-2016 models, identifying a batch of ignition coils from a specific supplier (YUMEBISHI) that were prone to internal failure, especially with large temperature changes. The TSB notes that good coils are made by MITSUBISHI. This is the most common cause of a P0302 code on these vehicles.
   How to confirm: Swap the ignition coil from cylinder 2 with another cylinder (e.g., cylinder 1). Cylinder 2 is the second from the front (belt side) of the engine. Clear the codes and drive. If the code returns as P0301, the coil is the confirmed culprit.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all four coils if the vehicle has high mileage or if they are the original, failure-prone YUMEBISHI type. Always replace the spark plug in the misfiring cylinder when replacing a coil.
   Est. part cost: $40-$100 per coil
2. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a regular maintenance item with a replacement interval of 75,000 miles (120,000 km) for the non-turbo 2.5L engine. The high-compression SkyActiv engine is sensitive to spark quality. An old, worn, or oil-fouled plug can easily cause a misfire. Oil fouling can occur due to a leaking spark plug tube seal, which is part of the valve cover gasket set.
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder 2. Inspect it for wear (worn electrode), carbon tracking, oil fouling, or a cracked insulator. A light brown or grey tip is normal. Compare it to a plug from a healthy cylinder.
   Typical fix: Replace the spark plug. It is best practice to replace all four spark plugs at the same time with high-quality OEM-spec Iridium plugs, such as NGK or Denso. The OEM NGK plug is model ILKAR7L11.
   Est. part cost: $60-$120 for a set of four Iridium plugs
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability TSBs #01-004-17-3317a and #01-017-16-3242 note that P0302 is often stored with fuel injector circuit codes like P0202. In some cases, this was caused by an internal failure of the PCM itself. Direct injectors can also become clogged from fuel deposits over time. One owner on a forum noted their cylinder 2 injector was "caked" with deposits, causing a P0302.
   How to confirm: Listen for a consistent clicking sound from the injector. A more advanced method is to measure the injector's resistance or swap it with another cylinder, though this is more labor-intensive than swapping a coil. A professional can perform a flow test.
   Typical fix: Clean or replace the fuel injector for cylinder 2. Replacing the injector seal is required during this service. If injector circuit codes (P0202) are present, the wiring or PCM may be at fault per TSBs.
   Est. part cost: $70-$200 per injector
4. Carbon Buildup on Intake Valves ⚪ Low Probability As a direct-injection engine, fuel is sprayed directly into the cylinder, so it does not wash over the intake valves. Over many miles (typically 100k+), oil vapor from the PCV system can bake onto the valves, restricting airflow and causing misfires, especially on cold starts.
   How to confirm: This requires visual inspection by removing the intake manifold. A borescope can be used to see the condition of the valves without full removal.
   Typical fix: Manual cleaning of the intake valves (walnut blasting is the professional standard) is required. This is a labor-intensive job, typically costing several hundred dollars in labor.
   Est. part cost: $100-$200 for gaskets and seals; shop labor is significant.

Rare But Worth Checking

• Frozen Water in Intake or Exhaust: Several TSBs (#01-007-19-3541, #01-006-18-3429, #01-002-17-3299a) mention that in cold climates where average drive time is low, water can accumulate and freeze in the intake or exhaust system (main silencer), causing a restriction and leading to misfire codes upon startup. The diagnosis involves checking freeze-frame data for low intake air temperatures at the time of the fault.
• Low Engine Compression: A mechanical issue like a burnt valve, worn piston rings, or a leaking head gasket can cause a loss of compression in cylinder 2, leading to a persistent misfire that does not resolve with ignition or fuel part swaps. A compression test is needed to diagnose this. One Reddit user with P0302 found oil on the spark plug, pointing towards a potential compression issue from oil burning.
• Leaking Valve Cover Gasket / Spark Plug Tube Seal: The valve cover gasket set includes seals for the spark plug wells. If the seal for cylinder 2 fails, oil can leak into the tube and short out the ignition coil and spark plug, causing a misfire. This would be visually obvious as pooled oil when removing the ignition coil.
• Faulty Powertrain Control Module (PCM): TSB #01-017-16 and #01-004-17-3317a state that for some 2014-2016 models, an internal failure of the DENSO-produced PCM could cause injector circuit codes (P0202/P0203) and associated misfire codes (P0302/P0303). This would require PCM replacement.

Diagnosis Steps

1. Read the code with an OBD-II scanner and check for any other stored codes, especially injector circuit codes (P0202).
2. Swap the ignition coil from cylinder 2 with cylinder 1. Cylinder 2 is the second from the front (belt side) of the engine.
3. Clear the codes and test drive the vehicle until the check engine light returns.
4. If the code is now P0301, the ignition coil is faulty and needs replacement. Inspect the old coil for the YUMEBISHI brand name, which is known to be failure-prone per TSB 01-014/16.
5. If the code remains P0302, remove the ignition coil and inspect the spark plug well for any oil. Oil presence indicates a leaking valve cover or spark plug tube seal.
6. If no oil is present, swap the spark plug from cylinder 2 with cylinder 1. Repeat the test drive.
7. If the code is now P0301, the spark plug was the issue. Replace all four plugs with OEM-spec Iridium plugs.
8. If the code remains P0302, the problem is likely with the fuel injector, wiring, or a mechanical issue.
9. Inspect the wiring and connector for the cylinder 2 fuel injector and ignition coil for any damage.
10. If no obvious issues are found, consider a professional diagnosis, which may include a fuel injector test, a compression test, or a leak-down test to check for mechanical engine problems.

Parts You'll Likely Need

• Ignition Coil

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or begins to affect other cylinders, a P0300 (Random Misfire) code may appear alongside P0302. This can happen if the root cause is systemic, like a failing battery causing multiple electrical issues.
• P0202 — This code for 'Fuel Injector Circuit/Open - Cylinder 2' is directly linked to P0302. Mazda TSBs #01-004-17-3317a and #01-017-16-3242 state they are often stored together when the fuel injector, its wiring, or even the PCM is the root cause.
• P0301, P0303, P0304 — Misfire codes for other cylinders. If seen with P0302, it points towards a problem affecting the whole engine, like a major vacuum leak, failing fuel pump, or the frozen intake/exhaust issue noted in TSBs.

Technical Service Bulletins (TSBs) & Recalls

• 01-014/16: Addresses misfire codes P0300-P0304 caused by internal failure of specific YUMEBISHI-produced ignition coils.
• 01-007-19-3541: Notes that P0302 can be caused by frozen water in the intake system.
• 01-004-17-3317a: States that P0302 is usually stored at the same time as fuel injector circuit codes P0202 and P0203.
• 01-006-18-3429: Mentions P0302 may be caused by frozen water accumulation.
• 01-017-16-3242: Links engine misfire DTCs like P0302 with fuel injector circuit open codes like P0202.
• 01-002-17-3299a: Cites frozen water as a potential cause for P0302 and other misfire codes.

Platform-Specific Known Issues

• Ignition Coil Failures (TSB 01-014/16): 2014-2016 models may have ignition coils from a supplier named YUMEBISHI that are prone to failure. The TSB advises replacing them with updated parts.
• Frozen Water in Intake/Exhaust (Multiple TSBs): In very cold climates, water can freeze in the intake system or main silencer (muffler), causing an exhaust restriction and triggering misfire codes on a cold start. [TSB #01-007-19-3541, TSB #01-006-18-3429, TSB #01-002-17-3299a, 15]
• Fuel Injector Circuit Faults (Multiple TSBs): TSBs #01-004-17-3317a and #01-017-16-3242 specifically mention that P0302 can be caused by a fuel injector circuit problem, which would also set a P0202 code. [TSB #01-004-17-3317a, TSB #01-017-16-3242]
• Carbon Buildup: Owners have reported P0302 misfires around 60,000 miles caused by significant carbon buildup on the intake valves, a known side effect of direct-injection engines.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.49 - 0.57 Ohms 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 kOhms. Failure: A reading outside this range indicates a faulty coil.
• Fuel Injector Resistance (Direct Injection) — expected: 1.74 - 2.04 Ohms at 20°C (68°F). Failure: A reading of 0 (short) or OL (open) indicates a faulty injector. Readings should be consistent across all injectors.
• High-Pressure Fuel System Pressure (at idle) — expected: Approx. 3.0 MPa {31 kgf/cm², 435 psi}. Failure: Significantly lower pressure could indicate a failing high-pressure fuel pump, though this would likely cause multiple/random misfires.

Hidden / Shadow Codes Worth Checking

• Mode 6, TID $A2-$A5: Misfire counts for each cylinder (Cylinder 1-4). While not a 'hidden code', this data is not always displayed on basic scanners but can be accessed with more advanced tools. It shows the raw number of misfire events the PCM has counted for each cylinder, which is useful for confirming an intermittent misfire before the CEL is triggered. (see via Advanced OBD-II scanner or professional tool like Mazda M-MDS with Mode 6 test capability.)

Scan Tool Commands That Help

• Mazda M-MDS (or equivalent): Power Balance Test — This active test allows a technician to sequentially disable the fuel injector for each cylinder. When the injector for a healthy cylinder is disabled, the engine RPM will drop noticeably. If disabling the cylinder 2 injector causes little or no change in RPM, it confirms that cylinder 2 is not contributing power.
• Mazda M-MDS (or equivalent): PID: FUEL_PRES — Used to monitor the live fuel pressure from the high-pressure fuel sensor. This helps verify if the fuel system is maintaining the target pressure of approximately 435 psi at idle.

Wiring & Ground Locations

• Ignition Coil Connector — Directly on top of each ignition coil, secured to the valve cover.. The 4-pin connector supplies 12V power, ground, and the trigger signal from the PCM. Corrosion or a loose connection at the cylinder 2 coil connector can cause a P0302. The connector itself can be replaced if the locking tab is broken or pins are damaged.
• PCM Connector (Ignition Control) — The Powertrain Control Module (PCM) is located in the engine compartment. The specific pin for the cylinder 2 coil trigger signal would need to be identified from a model-year specific wiring diagram.. A wiring fault between the PCM and the cylinder 2 ignition coil connector can cause a misfire. A technician can test for continuity and voltage at the PCM pin to rule out a wiring harness issue or a failed PCM driver.
• Engine Ground Strap — There are multiple ground points. A key ground is typically located on the left side of the engine compartment, connecting the engine block/transaxle to the chassis.. A poor engine ground can cause a wide range of electrical issues, including weak spark across all cylinders. While it would typically cause a random misfire (P0300), it can sometimes manifest as a single-cylinder misfire initially if one coil's connection is more marginal than others.

Real Owner Repair Stories

• Reddit user in r/mazda (2007 Mazdaspeed 6 (162k miles)) — Persistent P0302 misfire on cylinder 2.
  ❌ Tried (didn't work) Replaced all ignition coils, Replaced all spark plugs, Replaced all fuel injectors, Replaced timing chain and VVT, Confirmed good compression, Cleaned carbon from intake valves
  ✅ What actually fixed it The owner discovered that the brand new ignition coil they had installed on cylinder 2 was defective out of the box. Replacing the new, faulty coil with another new one resolved the misfire.
• Mazdaspeeds.org forum user (2007 Mazdaspeed 6) — P0302, rough idle, stuttering under acceleration, flashing CEL.
  ❌ Tried (didn't work) New spark plugs (NGK 3787), New ignition coil (and swapped coils between cylinders), Cleaned and flow-tested injectors, Replaced camshaft position sensor, Confirmed good compression
  ✅ What actually fixed it After removing the fuel injectors for inspection, the owner found the cylinder 2 injector was completely 'caked' with deposits, blocking the spray holes. Replacing the fuel injectors and cleaning the intake valves while they were accessible fixed the P0302 code.

OEM Part Supersession History

• PE20-18-100 (YUMEBISHI) → PE20-18-100A, PE20-18-100B (MITSUBISHI) — The original YUMEBISHI-produced coils were prone to internal failure due to high temperature differentials, as noted in TSB 01-014/16.
  Heads up: The YUMEBISHI coils can be identified by a 4-digit lot number, while the improved MITSUBISHI coils have a 5-digit lot number. The TSB advises replacing any YUMEBISHI coils made before lot number 6328 (March 28, 2016).

Model Year Variations Within This Range

• 2014-2016: These model years are specifically called out in TSB 01-014/16 as being equipped with the failure-prone YUMEBISHI ignition coils. While a 2017 model could have a failed coil, it is less likely to be related to this specific manufacturing defect.
• 2014-2016: TSBs #01-017-16 and #01-004-17-3317a mention an internal PCM failure on some models that could cause injector circuit codes (P0202) and associated misfires (P0302). This seems to be isolated to earlier years of the generation.