P0303 on 2021-2025 Genesis GV80 3.5T: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2021-2025 Genesis GV80

Unlike the 2.5T four-cylinder engine in the GV80, which frequently gets this code due to a software glitch requiring a dealer update, the P0303 code on the 3.5T V6 almost always indicates a genuine hardware problem. While standard ignition component failure is common, this specific engine has also shown a pattern of fuel injector failures that can cause a persistent misfire on a single cylinder. Diagnostically, all six cylinders on the 3.5T V6 in the GV80 are relatively easy to access for ignition coil and spark plug service, which is not the case for all vehicles using this engine family.

Symptoms You May Notice

• Rough or vibrating idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Solid or flashing Check Engine Light
• Reduced fuel economy
• Smell of gasoline from the exhaust

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are a common failure point on modern direct-injection engines due to high heat and vibration. This is the most likely hardware failure causing a single-cylinder misfire.
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1). Clear the codes and drive. If the misfire code changes to P0301, the ignition coil is faulty. This is the universally recommended first diagnostic step.
   Typical fix: Replace the failed ignition coil. It's a simple unbolt-and-unplug procedure. Many owners replace the corresponding spark plug at the same time.
   Est. part cost: $90-$130
2. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug Spark plugs are a regular maintenance item with a 42,000-mile replacement interval. The high cylinder pressures in turbocharged GDI engines can shorten their effective lifespan or lead to fouling.
   How to confirm: After ruling out the ignition coil, remove the spark plug from cylinder 3. Inspect it for wear (worn electrode), damage, or heavy carbon/oil fouling. A worn plug is a very common cause for misfires under load.
   Typical fix: Replace the spark plug. It is best practice to replace all six spark plugs as a set if they are near their service interval to ensure consistent performance.
   Est. part cost: $25-$40 per plug
3. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Gasoline Direct Injection (GDI) injectors operate under extremely high pressure and can be susceptible to clogging or electrical failure. A pattern of injector failures has been noted by owners and technicians for the 3.5T engine, sometimes at low mileage.
   How to confirm: This is more difficult for a DIYer but has key indicators. A critical sign is a strong smell of raw gasoline on the oil dipstick, which points to a leaking injector. A professional can perform a fuel injector balance test or, as seen in technician videos, test the injector's resistance with a multimeter to find an open circuit.
   Typical fix: Replace the faulty fuel injector. This is a more labor-intensive job that may require professional service.
   Est. part cost: $150-$250

Rare But Worth Checking

• Leaking Valve Cover Gasket: → Shop Engine Valve Cover If the valve cover gasket fails, oil can leak into the spark plug tube, fouling the spark plug and destroying the ignition coil. When removing the coil, check for engine oil in the spark plug well.
• Carbon Buildup on Intake Valves: As a GDI engine, fuel does not spray over the intake valves to clean them. Over time (typically 60,000+ miles), carbon can build up, restrict airflow to a cylinder, and cause misfires. This is a known issue on the related 3.3T engine.
• Low Compression: In very rare cases on a newer vehicle, a persistent misfire can be caused by internal engine mechanical failure, such as a bad piston ring or a problem with a valve. This would be diagnosed with a compression test after all other possibilities are exhausted.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0303 and check for any other codes.
2. Identify cylinder 3. On the GV80 3.5T, this is the middle cylinder on the passenger side (Bank 1), between the front and rear cylinders.
3. Perform an ignition coil swap. Exchange the ignition coil from cylinder 3 with one from an easily accessible cylinder (e.g., cylinder 1, front passenger side).
4. Clear the codes, drive the vehicle, and re-scan. If the code has moved to the other cylinder (e.g., P0301), the ignition coil is the faulty part.
5. If the code remains P0303, the coil is likely good. Next, inspect the spark plug from cylinder 3 for wear or fouling. Consider swapping the spark plug with another cylinder to see if the misfire follows.
6. If the coil and spark plug are confirmed good, check the oil dipstick. A strong smell of raw gasoline is a critical indicator of a leaking GDI fuel injector. Do not drive if this is observed.
7. If an injector is suspected, professional diagnosis is recommended. A technician can confirm the failure by testing the injector's electrical resistance or performing a flow test.
8. If the problem persists, a compression test may be needed to rule out rare mechanical engine issues.

Parts You'll Likely Need

• Ignition Coil (OEM #27301-3L100 (or 27310-3N290)) — This is the most common hardware failure causing a single-cylinder misfire on the 3.5T engine. The part number 27301-3L100 is a revised part that supersedes older numbers.
  Trusted brands: Genesis Genuine, Bosch, NGK, Delphi
  OEM price range: $90-$130
  Aftermarket price range: $60-$100
• Spark Plug (OEM #18877-09085) — Spark plugs are a routine maintenance item and the second most likely cause of a misfire if the ignition coil is good.
  Trusted brands: NGK, Denso
  OEM price range: $25-$40
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes intermittent or starts to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0303.
• P219E — A code for 'Cylinder #3 Air-Fuel Ratio Imbalance' could appear, pointing more directly towards a fuel injector problem rather than an ignition issue.
• P0363 — This code for 'Misfire Detected – Fueling Disabled' may appear with a severe, continuous misfire. The ECM cuts fuel to the misfiring cylinder (in this case, #3) to protect the catalytic converter, confirming the severity of the issue.

Platform-Specific Known Issues

• A pattern of fuel injector failures has been observed by technicians and owners on the 3.5T engine, which can cause a persistent P0303 code that is not resolved by replacing ignition components.
• Some 2021-2023 GV80 models were recalled for a low-pressure fuel pump that could fail and cause a loss of power (NHTSA Recall 23V630000). While this typically causes multiple misfire codes (P0300), it is a known fuel system weakness that can present as hesitation or stalling.

Mechanic-Grade Diagnostic Values

• GDI Fuel Injector Resistance — expected: ~1.9 - 2.2 Ohms. Failure: An open circuit (OL), a reading in the kOhm range, or a variance of more than ~0.3 Ohms from other injectors.
• Ignition Coil Primary Winding Resistance — expected: ~0.8 - 1.2 Ohms. Failure: A reading significantly outside this range or an open circuit (OL).
• Ignition Coil Secondary Winding Resistance — expected: ~6 - 10 kOhms. Failure: A reading significantly outside this range or an open circuit (OL).
• Low-Pressure Fuel System (LPFP) Pressure — expected: ~50 - 80 PSI. Failure: Pressure significantly below 50 PSI can indicate a failing in-tank fuel pump, which is subject to a recall.
• High-Pressure Fuel System (HPFP) Pressure at Idle — expected: 2,000 - 2,500+ PSI. Failure: Pressure that fails to build to specification can indicate a failing high-pressure fuel pump.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $A2-$AF: These test IDs store the raw, unprocessed misfire counts for each cylinder. This data is more sensitive than the threshold required to set a P030x code, allowing a technician to see small or intermittent misfires before they trigger a Check Engine Light. (see via An advanced OBD-II scan tool with Mode $06 capability.)

Scan Tool Commands That Help

• Genesis GDS (Global Diagnostic System): Cylinder Power Balance Test — To definitively isolate the misfiring cylinder. The tool deactivates each cylinder one by one; if deactivating cylinder 3 causes no change in engine RPM, it confirms that cylinder is not contributing power.
• Genesis GDS (Global Diagnostic System): Actuation Test (Fuel Injector) — To command the cylinder 3 injector to fire and measure the corresponding drop in fuel rail pressure. This helps isolate a clogged or weak injector without having to physically remove it first.
• Genesis GDS (Global Diagnostic System): Resetting Adaptive Values — After replacing a component like a fuel injector, this function should be used to clear the ECM's long-term learned fuel trims, allowing the system to adapt to the new part's characteristics more quickly.

Wiring & Ground Locations

• Bank 2 Injector/Coil Ground — On the intake manifold itself, providing a ground path for the driver's side (Bank 2) components.. While P0303 is for Bank 1, a loose or corroded ground on the opposite bank's manifold is a known pattern for causing intermittent, hard-to-diagnose misfires on related Hyundai/Genesis V6 engines. It highlights the importance of checking all major engine grounds when diagnosing persistent electronic issues.
• SENSOR2 Fuse — In the main engine compartment fuse box.. This 15A fuse provides power to the ignition coils for the 3.5T engine. While a blown fuse would likely cause multiple misfire codes, checking it is a quick and easy step to rule out a power supply issue to the coils.

Real Owner Repair Stories

• YouTube channel 'THE CAR GUY' (2021 Genesis GV80 3.5T) — Persistent check engine light with misfire codes P0302 and P0304 after a previous repair.
  ❌ Tried (didn't work) The vehicle had a history of misfires, and the technician suspected an injector based on prior experience with the car.
  ✅ What actually fixed it The technician tested the resistance of the fuel injectors and found one with an open circuit (injector #2) and another with a resistance reading that was 0.3 Ohms lower than a known-good injector (injector #4). Replacing the faulty injectors and all six spark plugs resolved the misfires.

OEM Part Supersession History

• 27310-3N290 → 27301-3L100 — Part revision and consolidation by the manufacturer. The newer part is specified for a wider range of Hyundai/Genesis/Kia models.

Model Year Variations Within This Range

• 2022-2023: For the 2022 model year, Genesis expanded the standard fitment of front-wheel monoblock brake calipers to the 2.5T and 3.0D models, and added a copper color caliper option for the 3.5T. While not directly related to P0303, it marks a minor production change.
• 2024-present: A facelift was introduced for the 2024 model year, which included a GV80 Coupe variant. The coupe offers an optional higher-powered 3.5T engine with a 48V electric supercharger. This 'e-S/C' version has a different engine code and power output, and its diagnostics may differ slightly.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Rear Differential Whine/Hum 🟠 Medium — Common issue reported by many owners, typically noticeable between 40-60 mph under light throttle. Can occur at low mileage. (Ref: TSB 23-DS-004G instructs dealers to first attempt to retorque a pinion nut; if that fails, the entire differential assembly is replaced.)
• Low-Pressure Fuel Pump Failure 🔴 High → Shop Fuel Pump — Affects a significant number of 2021-2023 models, leading to a recall. The impeller can deform, causing fuel starvation and sudden loss of power. (Ref: NHTSA Recall 23V630000 (Genesis Campaigns 016G/022G) and its expansion 24V282 cover this issue, requiring replacement of the fuel pump assembly.)
• Infotainment/Instrument Cluster Blank Screen or Reboot 🟡 Low — Widespread software glitches can cause the main 14.5-inch display and/or the digital instrument cluster to freeze, go blank, or reboot intermittently. (Ref: Often resolved by a soft reset (holding MAP + SETUP buttons) or a dealer software update. NHTSA Recall 25V-105 was issued for 2023-2024 models for the instrument cluster going blank.)
• Potential for Connecting Rod Bearing Failure 🔴 High — While more famous on older Hyundai/Genesis engines, the company has procedures (TSB 21-EM-004H-1) for a 'Bearing Clearance Test' on newer engines, indicating continued monitoring for premature bearing wear. (Ref: Related to multiple prior Hyundai/Genesis engine recalls (e.g., Recall 198). A knocking sound or oil pressure light should be investigated immediately.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: Used parts are generally not recommended for fixing a P0303 code on this vehicle due to the nature of the common failure items. However, a low-mileage ignition coil from a reputable salvage yard could be a cost-effective diagnostic tool to confirm a failure before buying a new part.

Donor-vehicle mileage cap: roughly under 30000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For an ignition coil, ensure there is no cracking in the plastic housing or corrosion on the electrical connector.
• Check for any signs of oil contamination on the boot, which would indicate the donor vehicle had a leaking valve cover gasket.
• Verify the part number on the used part matches the OEM number for your vehicle.

OEM-only on this vehicle (don't cheap out):

• Fuel Injector: GDI injectors are high-precision, high-pressure components. Aftermarket versions have a high rate of premature failure. Given the pattern of injector issues on this engine, using only Genesis Genuine parts is critical to ensure proper function and longevity.
• Spark Plugs: While not strictly 'OEM-only', using the specified NGK or Denso Iridium plugs is crucial. Incorrect heat ranges or plug gaps can cause persistent misfires, especially in this turbocharged GDI engine.

Aftermarket brands forum-validated for this vehicle:

• Ignition Coils: NGK, Delphi, Bosch are widely trusted OEM-quality suppliers for ignition components.

Brands owners have reported issues with on this vehicle:

• Unbranded, 'white box' ignition coils and fuel injectors from online marketplaces should be avoided. These often use inferior materials and lack the quality control of established brands, leading to repeat failures.

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 or Multiple Cylinder Misfire Detection; often triggered by the low-pressure fuel pump failure (Recall 23V630000) affecting the entire fuel rail.
• P0301 — Cylinder 1 Misfire; the code that appears if you successfully swap a faulty ignition coil from cylinder 3 to cylinder 1 during diagnosis.
• P0302 — Cylinder 2 Misfire; frequently seen alongside other cylinder codes in the 3.5T engine when multiple GDI injectors fail simultaneously.
• P0304 — Cylinder 4 Misfire; documented in technician case studies as a companion code to other misfires caused by faulty GDI injectors on this platform.

Frequently Asked Questions