P0303 on 2019-2025 Genesis G70 3.3T V6: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2019-2025 Genesis G70

While owners of other Genesis models (with the 2.5T 4-cylinder engine) may find service bulletins for software updates to fix false misfire codes, this does not apply to the 3.3T V6. For the G70 3.3T, a P0303 code indicates a genuine hardware problem. The key challenge on this platform is the location of cylinder 3; it is on the rear bank of the V6 engine, close to the firewall. Accessing this cylinder's ignition coil and spark plug for diagnosis and repair requires the removal of the upper intake manifold, making it significantly more difficult and time-consuming than working on the front cylinders (2, 4, 6). This difficult access is the primary driver of higher repair costs for this specific code.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Solid or flashing Check Engine Light
• Potential fuel smell from the exhaust
• Decreased fuel economy

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Owner forums for both the G70 and its platform-mate, the Kia Stinger, are replete with examples of ignition coil failure causing P0303, sometimes at relatively low mileage (e.g., 19k, 55k miles). The high heat environment at the rear of the engine bay, near the firewall and turbochargers, may contribute to premature failure of the cylinder 3 coil.
   How to confirm: The standard method is to swap the cylinder 3 ignition coil with another cylinder's coil. However, given cylinder 3's location on the difficult-to-access rear bank, this is not a simple DIY task as it requires removing the intake manifold. 🎬 Watch: A clever DIY trick to change plugs without removing the intake. A professional diagnosis will follow this same logic after accessing the coils. If the code moves to the swapped cylinder (e.g., P0302 after swapping with cylinder 2), the coil is confirmed bad.
   Typical fix: Replace the faulty ignition coil (Part No. 27310-3L000). It is highly recommended to replace the corresponding spark plug at the same time. Many owners and technicians recommend replacing all three rear bank coils and all six spark plugs while the intake manifold is removed to avoid repeated labor costs.
   Est. part cost: $50-$100
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item with a recommended replacement interval of 42,000 miles on the 3.3T engine. A failing ignition coil can also quickly foul a spark plug with carbon or fuel, causing it to fail. Given the labor required to access the rear plugs, they are sometimes neglected, leading to misfires as they exceed their service life.
   How to confirm: After removing the intake manifold to gain access, remove the spark plug from cylinder 3 and inspect it. Look for a worn electrode, cracked ceramic, or heavy black carbon/fuel deposits. A Reddit user's technician noted a 'bllllackkkkk' spark plug when diagnosing a P0303.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs as a set to ensure even performance, especially since the intake manifold must be removed to access the rear three. Use OEM or equivalent Iridium plugs (e.g., NGK).
   Est. part cost: $15-$30 per plug
3. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector While less common than ignition issues, GDI (Gasoline Direct Injection) injectors can become clogged or fail electronically. This is a known, though less frequent, issue on Hyundai/Kia GDI engines.
   How to confirm: This is more difficult to diagnose and usually done after ruling out ignition components. A professional can perform a fuel injector balance test. A strong smell of gasoline on the oil dipstick is a critical symptom of a leaking GDI injector, which can lead to catastrophic engine damage if ignored.
   Typical fix: Replace the faulty fuel injector. This is an involved job, especially on the rear bank, and professional service is strongly recommended.
   Est. part cost: $80-$200

Rare But Worth Checking

• Low Engine Compression: In rare cases on higher mileage engines, a mechanical issue like a burnt exhaust valve or piston ring failure could cause a persistent misfire. This would be diagnosed with a compression test after ruling out all ignition and fuel causes.
• Carbon Buildup on Intake Valves: As a direct-injection (GDI) engine, the Lambda II 3.3T is susceptible to carbon buildup on the back of the intake valves over time, as fuel is not sprayed over them to keep them clean. Severe buildup can disrupt airflow into the cylinder and cause misfires, typically on higher-mileage vehicles (60k+ miles).

Diagnosis Steps

1. Read the codes: Use an OBD-II scanner to confirm P0303 is the primary code. 🎬 See this helpful walkthrough on diagnosing and fixing a P0303 code. Note any other codes (e.g., P0300, P0301, P0305).
2. Assess the Check Engine Light: If the light is flashing, shut off the engine as soon as safely possible to prevent catalytic converter damage.
3. Confirm Cylinder Location: Cylinder 3 is on the passenger side (Bank 1), in the middle position, against the firewall. Acknowledge that access requires significant disassembly.
4. Professional Diagnosis Recommended: Due to the need to remove the upper intake manifold to access cylinder 3, this is not a simple roadside diagnostic. A shop is the recommended path.
5. Shop Diagnostic Procedure: A technician will first remove the engine cover, strut braces, and then the upper intake manifold. Once accessed, they will likely perform a 'swap test' by moving the cylinder 3 coil to an adjacent rear cylinder (e.g., cylinder 1) and reinstalling the manifold just enough to run the engine. If the code changes to P0301, the coil is bad.
6. Inspect and Replace: If the coil is the culprit, it will be replaced. Regardless, the spark plug in cylinder 3 should be removed, inspected, and likely replaced. It is best practice to replace all three rear coils and all six spark plugs at this stage to prevent future labor.
7. Further Diagnosis: If the misfire persists on cylinder 3 after replacing the coil and plug, the technician will then investigate the fuel injector and wiring, and may perform a compression test to check for mechanical engine issues.

Parts You'll Likely Need

• Ignition Coil (Rear Bank) (OEM #27310-3L000) — This is the most common failure part for a P0303 code on this engine. The rear bank uses a different coil from the front. This part fits G70, Stinger, G80, and G90 with the 3.3T engine.
  Trusted brands: Hyundai/Genesis (OEM), Delphi, Denso
  OEM price range: $60-$100
  Aftermarket price range: $40-$80
• Spark Plug (OEM #18852-09070) — This is a primary ignition component and a scheduled maintenance item (42k miles). It is often replaced with the coil as a set.
  Trusted brands: Hyundai/Genesis (OEM), NGK (Often the OEM supplier) 🎬 Watch this quick video for a step-by-step spark plug installation guide.
  OEM price range: $25-$35
  Aftermarket price range: $15-$25
• Ignition Coil (Front Bank, for reference) (OEM #27310-3L030) — For reference only. This part is for the easily accessible front cylinders (2, 4, 6) and is NOT interchangeable with the rear coil.
  Trusted brands: Hyundai/Genesis (OEM)
  OEM price range: $60-$100
  Aftermarket price range: $40-$80

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or starting to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0303.
• P0301, P0305 — Misfire codes for other cylinders on the same bank (Bank 1) could indicate a problem common to that bank, such as a vacuum leak affecting that side of the intake manifold or a batch of failing coils.

Technical Service Bulletins (TSBs) & Recalls

• TSB 24-01-032G: This technical service bulletin addresses a recall for the left-hand turbocharger oil feed pipe on 2019-22 G70 3.3T models. The cause is cited as prolonged exposure to high ambient temperature in the engine compartment. This corroborates the harsh heat environment for rear-bank components like the cylinder 3 ignition coil.

Platform-Specific Known Issues

• Owner Experience: Coil Failure at 47k Miles: A user on the r/GenesisG70 subreddit reported doing a spark plug change at 47,000 miles and had the boot for the ignition coil tear while trying to remove it, indicating it was seized on the plug. This highlights that even during routine maintenance, the coils can be problematic.
• Owner Experience: Multiple Coil Failures: A 2020 G70 owner on Reddit reported needing to replace two ignition coil packs as part of a list of issues on a car with 55,000 miles, corroborating that these are a known failure item.

Mechanic-Grade Diagnostic Values

• High-Pressure Fuel Pump (HPFP) Outlet Pressure — expected: Over 2,500 PSI under load. Failure: Significantly lower pressure readings can indicate a failing HPFP, leading to fuel starvation and misfires.
• Low-Pressure Fuel Pump (In-Tank) Outlet Pressure — expected: Approximately 50-80 PSI. Failure: Pressure below this range indicates a weak in-tank pump, which will starve the HPFP and cause misfires under load.

Scan Tool Commands That Help

• Genesis GDS (or equivalent professional scanner): Misfire Counter / Power Balance Test — This live data function is the primary tool to see which cylinder is actively misfiring in real-time, confirming the P0303 code corresponds to a current fault on cylinder 3 before beginning disassembly.
• Genesis GDS (or equivalent professional scanner): Injector Activation Test — If a misfire remains on cylinder 3 after swapping ignition coils and spark plugs, this bidirectional command can be used to individually cycle the cylinder 3 fuel injector to check for an audible click, helping to identify a dead or stuck injector without removal.
• Genesis GDS (or equivalent professional scanner): Fuel Pump Relay Actuation Test — This test is used to command the low-pressure fuel pump on, verifying the integrity of the relay and its circuit when diagnosing a potential fuel delivery issue that could cause a misfire.

Wiring & Ground Locations

• Ignition Coil Connector — On top of each ignition coil, secured by a 10mm bolt to the valve cover.. The connector for cylinder 3 is difficult to access. It has a grey safety clip that must be pulled back before the connector can be unplugged. A poor connection here will cause a P0303.
• Engine Control Unit (ECU) — Located in the engine bay on the driver's side, just ahead of the brake fluid reservoir and next to the strut tower.. This is the source of the signal to the ignition coil and fuel injector. While rare, an ECU driver failure can cause a persistent single-cylinder misfire. All wiring for the ignition and fuel systems terminates here.

Real Owner Repair Stories

• Reddit user in r/GenesisG70 (Genesis G70 3.3T (year not specified)) — Check engine light with code P0303, indicating a cylinder 3 misfire.
  ❌ Tried (didn't work) The owner took the vehicle directly to the dealer for diagnosis.
  ✅ What actually fixed it The dealership diagnosed and replaced the faulty ignition coil pack for cylinder 3.
• Reddit user in r/GenesisGV70 (2025 GV70 (likely 3.5T, but same diagnostic principle)) — Check engine light with code P0303 at 14,000 miles.
  ❌ Tried (didn't work) The owner initially thought it was a recall issue seen on other models.
  ✅ What actually fixed it The dealer diagnosed a bad coil pack. The technician also noted the spark plug was 'bllllackkkkk,' indicating it was fouled as a result of the bad coil. The dealer ordered the new coil pack for the fix.

OEM Part Supersession History

• 27310-3L000 → No official supersession found. — This part number appears to be the consistent OEM part for the rear bank ignition coil across the model years.
  Heads up: Aftermarket high-performance coils are available from brands like Worms Racing, which claim to provide over 10% more spark energy. These are plug-and-play but are typically for tuned vehicles.

Model Year Variations Within This Range

• 2022-2025: The 2022 model year introduced a facelift with revised styling and a larger 10.25-inch infotainment screen. For the 3.3T engine, an optional variable-valve active exhaust was added, which slightly increases horsepower. However, the core engine, ignition system, and fuel system architecture related to a P0303 code remained unchanged from the 2019-2021 models.
• 2021+: Starting with the 2021 G70, premium fuel (91 octane or higher) is required. While using lower octane fuel won't directly cause an immediate P0303, it can lead to reduced performance and, over time, contribute to conditions like carbon buildup that may cause misfires.

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 alongside P0303 if multiple coils are failing or if a broader issue like a clogged GDI fuel injector affects the engine.
• P0301 — Cylinder 1 Misfire Detected. This code will appear during a shop diagnostic 'swap test' if the technician moves the faulty cylinder 3 ignition coil to cylinder 1 to confirm the coil is bad.
• P0302 — Cylinder 2 Misfire Detected. Similar to P0301, this code will trigger if the faulty cylinder 3 ignition coil is swapped to cylinder 2 during the diagnostic process.
• P0305 — Cylinder 5 Misfire Detected. Explicitly noted in the diagnostic steps as a companion misfire code to look out for when scanning the vehicle's OBD-II system.

Frequently Asked Questions