P0302 on 2016-2019 Mazda CX-3: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2016-2019 Mazda CX-3

The 2016-2019 Mazda CX-3 uses the reliable 2.0L Skyactiv-G engine. While generally robust, this direct-injection engine can be susceptible to issues that cause misfires. Mazda has issued Technical Service Bulletins (TSBs) for this platform related to misfires caused by frozen water in the exhaust restricting flow in cold climates (TSB #01-007-19-3541). Additionally, TSBs for other Skyactiv models highlight potential issues with fuel injector circuits (TSB #01-004-17-3317a) and carbon buildup on intake valves, which can also lead to misfire codes like P0302. A Reddit user with a 2016 CX-3 at 72,500 miles reported a P0302 that was ultimately fixed by replacing a faulty fuel injector.

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
• Reduced engine power
• Flashing check engine light (indicates a severe misfire that can damage the catalytic converter)
• Decreased fuel economy
• Engine stalling
• Smell of burning electrical components from the engine bay, pointing to a failed ignition coil

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a common wear item on most modern engines. Heat and vibration eventually cause the internal windings to fail. Multiple owners on forums report P0302 being resolved by replacing the cylinder 2 coil.
   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 faulty. A failed coil may also have visible signs of damage, like a bubble or burnt spot on its housing.
   Typical fix: Replace the faulty ignition coil. It's often recommended to replace all four if they are original and the vehicle has high mileage.
   Est. part cost: $25 - $75 for one aftermarket coil
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Mazda recommends replacing the spark plugs at 75,000 miles. Plugs that are worn past this interval or fouled by oil or carbon can fail to produce a strong enough spark, causing a misfire.
   How to confirm: Remove the spark plug from cylinder 2 and inspect it. Look for a worn electrode, heavy black carbon deposits, or oil fouling. Compare it to a plug from another cylinder. You can also swap the plug with another cylinder to see if the misfire follows the plug.
   Typical fix: Replace the spark plug. Mazda specifies iridium spark plugs for the Skyactiv engine. It is best practice to replace all four spark plugs at the same time. The OEM plugs are made by NGK and Denso.
   Est. part cost: $40 - $80 for a set of four iridium plugs
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector As a direct-injection engine, the fuel injectors operate under high pressure and can be prone to clogging or electrical failure over time. A Reddit user with a 2016 CX-3 confirmed their P0302 was caused by a bad injector at 72,500 miles. TSB #01-004-17-3317a also notes that injector circuit codes (like P0202) can appear with misfire codes due to an internal PCM failure on some models.
   How to confirm: Listen to the injector with a mechanic's stethoscope to ensure it's clicking. You can also test the injector's resistance with a multimeter or have a professional perform a flow test. Swapping injectors between cylinders is a more involved but definitive diagnostic step. 🎬 See these expert tips for removing Skyactiv fuel injectors.
   Typical fix: Clean or replace the fuel injector for cylinder 2. In a documented case, a mechanic replaced all four injectors to resolve the issue.
   Est. part cost: $50 - $150 for one aftermarket injector
4. Carbon Buildup on Intake Valves ⚪ Low Probability Direct-injection (GDI) engines like the Skyactiv-G spray fuel directly into the cylinder, so gasoline detergents don't wash over the intake valves. Oil vapor from the PCV system can bake onto the valves, restricting airflow and causing misfires, especially on cold starts. A Mazda owner on Reddit with a P0302 on a Skyactiv-G engine at 58k miles found significant carbon buildup to be the cause after ignition components were ruled out.
   How to confirm: This requires a visual inspection of the intake valves using a borescope or by removing the intake manifold. A misfire that occurs mainly on cold starts and disappears when warm can be a symptom.
   Typical fix: The intake valves need to be professionally cleaned, typically through walnut shell blasting. 🎬 Watch: How to perform a carbon cleaning on intake valves. Spray-in cleaners are generally not considered a permanent or effective solution.
   Est. part cost: $0 (service cost is labor, typically $400-$800)

Rare But Worth Checking

• Frozen Water in Exhaust: Mazda TSBs #01-007-19-3541 and #01-006-18-3429 mention that in freezing temperatures (below 32°F/0°C), water from short trips can accumulate and freeze in the muffler (main silencer), restricting exhaust flow and causing a rough idle and misfire codes (P0300, P0302, etc.) on startup. The fix involves replacing the main silencer with an updated part that has drain holes.
• Low Engine Compression: While rare on this engine, 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. A compression test and a cylinder leak-down test are needed to diagnose this.
• Internal PCM Failure: TSB #01-004-17-3317a, applicable to some earlier Skyactiv models, describes a scenario where an internal PCM failure can cause injector circuit codes (P0202, P0203) and accompanying misfire codes (P0302, P0303). This would be an unlikely cause if only P0302 is present.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner. Use the freeze frame data to see the engine conditions (RPM, load, temperature) when the misfire occurred.
2. Identify cylinder 2. On the 2.0L Skyactiv-G, it is the second cylinder from the front of the engine (the side with the belts).
3. Swap the ignition coil from cylinder 2 with the coil from cylinder 3. Clear the codes and run the engine. If the code changes to P0303, the ignition coil is bad.
4. If the code remains P0302, swap the spark plug from cylinder 2 with cylinder 3. You will need an 8mm socket for the coil bolt and a 14mm thin-walled spark plug socket. Clear codes and re-test. If the code moves to P0303, the spark plug is the issue.
5. If the misfire is still on cylinder 2, inspect the fuel injector wiring for damage. Listen for a steady clicking sound from the injector with the engine running using a mechanic's stethoscope.
6. Inspect for vacuum leaks around the intake manifold, particularly near the gasket for cylinder 2.
7. If the problem persists, consider more advanced diagnostics like checking fuel pressure and performing an engine compression test to rule out mechanical issues.
8. If you live in a cold climate and the issue occurs on cold starts after the vehicle was parked overnight, investigate the possibility of a frozen exhaust as described in Mazda TSB #01-007-19-3541.

Parts You'll Likely Need

• Ignition Coil (OEM #PE20-18-100A) — This is the most frequent cause of a single-cylinder misfire. It's a simple plug-and-play replacement held by a single 8mm bolt. 🎬 Watch: Step-by-step guide to changing spark plugs and coil packs.
  Trusted brands: NGK, Denso, Duralast, Decco
  OEM price range: $90 - $125
  Aftermarket price range: $25 - $75
• Iridium Spark Plug (OEM #PE5R-18-110) — Spark plugs are a routine maintenance item and a common cause of misfires. The Skyactiv engine requires specific iridium plugs for proper performance. Mazda's recommended service interval is 75,000 miles, but they can fail sooner.
  Trusted brands: NGK, Denso
  OEM price range: $20 - $30 per plug
  Aftermarket price range: $10 - $20 per plug

Related Codes That Often Appear With This One

• P0300 — If the misfire in cylinder 2 is intermittent or severe enough to affect engine timing, a P0300 (Random Misfire) code may also be stored.
• P0301, P0303, P0304 — If you see other cylinder misfire codes, it points to a problem affecting the whole engine, such as a vacuum leak, low fuel pressure, or significant carbon buildup across all cylinders.
• P0202 — This code for 'Fuel Injector Circuit/Open - Cylinder 2' directly points to an electrical problem with the injector in cylinder 2. TSB #01-004-17-3317a confirms that these codes are often stored together when the injector or PCM is the cause.

Technical Service Bulletins (TSBs) & Recalls

• 01-007-19-3541: Check engine light with P0300-P0304 due to frozen water in the main silencer.
• 01-006-18-3429: Similar to the above, notes rough idle and misfire DTCs on cold starts due to frozen water in the exhaust.
• 01-004-17-3317a: Notes that misfire DTCs (P0301-P0304) are often stored with fuel injector circuit DTCs (P0201-P0204).
• 01-002-17-3299a: Another TSB mentioning misfire codes caused by frozen water accumulation in the main silencer.

Platform-Specific Known Issues

• Frozen Main Silencer (Muffler): In climates with freezing temperatures, TSB #01-007-19-3541 describes how water can accumulate and freeze in the muffler, especially after short trips. This creates an exhaust restriction on the next cold start, causing rough idle and misfire codes like P0302. The official fix is to replace the muffler with an updated version containing drain holes.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 1.6–2.52 ohms at a temperature of 0—80 °C {32—176 °F}. Failure: A reading outside of this range, or an open/infinite reading, indicates a faulty injector coil.
• High-Pressure Fuel System Capability — expected: Up to 2,000 - 2,800 PSI. Failure: This is the pump's maximum capability; actual pressure is commanded by the PCM. Low pressure readings under load could indicate a weak high-pressure fuel pump, but would likely affect all cylinders.
• Ignition Coil Primary Winding Resistance — expected: ~0.49–0.57 ohms. Failure: A reading significantly outside this range suggests a faulty coil. Note: This is a general value and may not be exact for OEM part PE20-18-100A.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $A2-$AF, Component ID $02: Mode $06 data can reveal misfire counts per cylinder before they are high enough to trigger a Check Engine Light. The specific Test ID (TID) for misfire counts can vary by manufacturer and year (e.g., Ford often uses TID $53). On modern scanners, this data is often decoded from hexadecimal into plain language like 'Cylinder 2 Misfire Count'. (see via A professional scan tool or an advanced DIY scanner with Mode $06 capabilities (like FORScan for Mazda, or apps like Torque Pro paired with a compatible OBD-II adapter). Look for misfire data for the current or previous 10 driving cycles.)

Scan Tool Commands That Help

• Mazda IDS (or equivalent professional scanner): Power Balance Test — To confirm a misfire on a specific cylinder when the cause is not obvious. This function deactivates one cylinder at a time and measures the corresponding drop in RPM. A cylinder with a misfire will show little to no RPM drop when deactivated, confirming it wasn't contributing power.
• Mazda IDS (or equivalent professional scanner): Injector Test — To command a specific fuel injector to operate, allowing the technician to listen for its clicking sound or measure its effect on the system without the engine running. This helps isolate a dead or lazy injector.

Wiring & Ground Locations

• PCM Terminals 1DW and 1DX — These are pin locations on the main Powertrain Control Module (PCM) connector.. When diagnosing a related P0202 code, Mazda's service manual directs testing for shorts or open circuits between the cylinder 2 fuel injector connector and these specific PCM pins. Pin 1DW is the control signal from the PCM to the injector, and 1DX is the verification signal.
• Engine Bay Fuse Box — Located on the right side of the engine compartment (passenger side in LHD vehicles).. Contains relays and fuses critical to the ignition and fuel systems. The fuel injector relay is located here and should be inspected if multiple injectors are not working or if a P0202 code is present.

Real Owner Repair Stories

• Reddit user in r/MechanicAdvice (2016 Mazda CX-3, 72,500 miles) — Check Engine Light with code P0302.
  ❌ Tried (didn't work) Adding fuel system cleaner and clearing the code (the light returned).
  ✅ What actually fixed it A mechanic diagnosed a faulty fuel injector. All four fuel injectors were replaced with OEM parts, which resolved the issue.

OEM Part Supersession History

• p51b18100, pe0118100, pe0118100a, pe2018100 → PE20-18-100A — Part has been revised and updated by the manufacturer over time to improve reliability or sourcing.

Model Year Variations Within This Range

• 2018-2019: For the 2018 model year facelift, the 2.0L Skyactiv-G engine was updated with new edge-cut pistons and new high-pressure injectors. Power output increased slightly. While the fundamental design is the same, these component changes (especially injectors) may not be backward compatible with 2016-2017 models.