P0303 on 2022-2025 Genesis GV70 3.5T: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2022-2025 Genesis GV70

Unlike the related 2.5T four-cylinder engine which has a known software glitch causing false misfire codes (addressed by Service Campaign 914G), a P0303 on the 3.5T V6 is almost always a genuine hardware problem. The primary challenge for this engine is not the diagnosis, but the location. Cylinder 3 is on the rear bank of the V6, close to the firewall, which can make accessing its ignition coil and spark plug more labor-intensive than on the front-facing cylinders. This is a well-documented issue on the platform-mate Kia Stinger as well.

Symptoms You May Notice

• Rough or vibrating idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Check Engine Light is on and steady
• Check Engine Light is flashing (in severe cases)
• Reduced fuel economy
• Smell of raw fuel 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 heat and vibration. Forum and technician reports for the 3.5T engine and its 3.3T predecessor frequently point to a bad coil as the primary cause for a single-cylinder misfire, sometimes at low mileage (e.g., 19,000 miles).
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1, which is more accessible). Clear the codes and drive. If the code changes to P0301, the ignition coil is confirmed to be faulty.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all coils on the same bank, or at least the spark plug for that cylinder, at the same time.
   Est. part cost: $70-$170 (OEM)
2. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug Spark plugs are a regular maintenance item. A failing ignition coil can also quickly foul a spark plug with carbon or unburnt fuel, causing it to fail. One owner reported a technician found a 'bllllackkkkk' spark plug when diagnosing a P0303 code on a related G70.
   How to confirm: After ruling out the ignition coil, remove the spark plug from cylinder 3. Inspect it for signs of wear, heavy carbon buildup, oil, or fuel fouling. A black, sooty plug often points to the misfire.
   Typical fix: Replace the spark plug. Given the labor to access cylinder 3, it is highly recommended to replace all six spark plugs at the same time.
   Est. part cost: $25-$40 per plug (OEM)
3. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector Direct injection (GDI) engines operate at very high fuel pressures, and injectors can be susceptible to clogging or electronic failure. While less common than ignition issues, injector problems are a known and increasingly documented potential cause on this engine platform, sometimes leading to recurring misfires even after ignition parts are replaced.
   How to confirm: This is difficult to confirm without professional tools. A mechanic can perform a fuel injector balance test to measure the flow rate of each injector. A strong smell of fuel on the oil dipstick can also indicate a leaking injector. The presence of code P219E00 ('Cylinder #3 Air-Fuel Ratio Imbalance') alongside P0303 strongly suggests an injector fault.
   Typical fix: Replace the faulty fuel injector. This is a more labor-intensive job than a coil or plug replacement, especially for a cylinder on the rear bank.
   Est. part cost: $100-$250

Rare But Worth Checking

• Vacuum Leak: A vacuum leak near the intake manifold runner for cylinder 3 could lean out the air/fuel mixture and cause a misfire. This is less likely to affect only one cylinder but is worth checking, especially if the intake manifold was recently serviced.
• Low Compression: Extremely rare on a newer vehicle, but an internal engine issue like a bad valve or piston ring could cause a persistent P0303. This is the last thing to check after all ignition and fuel possibilities are exhausted.
• Carbon Buildup on Intake Valves: As a Gasoline Direct Injection (GDI) engine, the Lambda II 3.5T does not spray fuel over the intake valves, which allows carbon deposits from the PCV system to bake onto them over time. This typically becomes a problem at higher mileages (e.g., 60,000+ miles) and can restrict airflow to a specific cylinder, causing a misfire. A chemical intake cleaning or media blasting is the fix.

Diagnosis Steps

1. Confirm the code with an OBD-II scanner. Note if the Check Engine Light is steady or flashing.
2. If the light is flashing, limit driving to prevent catalytic converter damage.
3. Locate cylinder 3 on the passenger side of the engine, middle cylinder, near the firewall.
4. Swap the ignition coil from cylinder 3 with the coil from cylinder 1 (front-most cylinder on the same bank).
5. Clear the codes with the scanner and drive the vehicle until the Check Engine Light returns.
6. If the new code is P0301, the ignition coil is faulty and needs replacement.
7. If the code remains P0303, the coil is likely good. Proceed to inspect the spark plug.
8. Remove and inspect the spark plug from cylinder 3 for wear, damage, or fouling. Replace if necessary.
9. If the coil and plug are good but the P0303 code persists, the issue may be with the fuel injector or, rarely, a mechanical problem. Check the oil dipstick for a strong fuel smell, which points to a leaking injector. At this point, professional diagnosis with tools like a fuel pressure gauge or compression tester is recommended.

Parts You'll Likely Need

• Ignition Coil (OEM #27310-3N290) — This is the most frequent failure point for a single-cylinder misfire on the 3.5T V6 engine.
  Trusted brands: Hyundai/Genesis Genuine, Denso
  OEM price range: $70-$170
  Aftermarket price range: $50-$100
• Spark Plug (OEM #18877-09085) — A worn spark plug is a common cause of misfires, and a bad coil can foul a good plug, requiring its replacement anyway.
  Trusted brands: Hyundai/Genesis Genuine, NGK
  OEM price range: $25-$40
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or beginning to affect other cylinders due to a systemic issue (like a fuel delivery problem or multiple failing injectors), a P0300 'Random/Multiple Cylinder Misfire' code may appear alongside P0303.
• P219E00 — This code for 'Cylinder #3 Air-Fuel Ratio Imbalance' can be stored with P0303. On the related Kia Carnival with a similar 3.5L engine, this combination is noted in a TSB to point directly to a faulty high-pressure fuel injector.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: ~0.8 - 1.2 Ohms. Failure: A reading significantly outside this range, or an open circuit (OL), indicates a faulty primary coil winding.
• Ignition Coil Secondary Winding Resistance — expected: ~6 - 10 kOhms (kilo-ohms). Failure: A reading significantly outside this range, or an open circuit (OL), points to a failure in the secondary coil winding.
• GDI Fuel Injector Resistance — expected: ~2.1 - 2.2 Ohms. Failure: An open circuit (infinite resistance) or a significantly different reading (e.g., 9.7 kOhms) indicates a failed injector coil.
• Mode $06 Misfire Count — expected: A low count, ideally zero, for each cylinder during a drive cycle.. Failure: A high and incrementing count for Cylinder 3 confirms it is the source of the active misfire.

Scan Tool Commands That Help

• Genesis GDS (or equivalent professional scanner): Misfire Counter / Power Balance Test — This live data function allows a technician to see which specific cylinder is misfiring in real-time, confirming the P0303 code corresponds to an active event in cylinder 3. It is the primary tool to verify the misfire location before swapping parts.
• Genesis GDS (or equivalent professional scanner): Injector Activation Test — After swapping coils and plugs, if the misfire remains on cylinder 3, this bidirectional command can be used to individually fire the cylinder 3 injector to listen for an audible 'click', helping to determine if the injector is electronically functional.
• Genesis GDS (or equivalent professional scanner): Reset Adaptive Values — This is a mandatory step after replacing a fuel injector. It clears the long-term fuel trim adjustments the PCM learned to compensate for the old, faulty injector, ensuring the new part operates correctly from a clean baseline.

Real Owner Repair Stories

• Reddit user Malvarado98118 (2023 GV70 Sport Prestige) — Recurring check engine light with misfire codes.
  ❌ Tried (didn't work) Initial dealer visits did not resolve the issue, suggesting simple part swaps (like coils or plugs) were either not performed or were not the root cause.
  ✅ What actually fixed it The final fix required three separate dealer visits and was the replacement of two faulty fuel injectors (upper and lower).
• Reddit user in r/GenesisGV70 ('22 GV70 3.5T with ~30,000 miles) — Saved (not active) codes P0302, P0303, and P0300 found during a pre-purchase inspection. Live data showed one engine bank running lean (Fuel trim 10.9% vs 4.6%).
  ✅ What actually fixed it This was a pre-purchase inspection, so no fix was performed. However, forum comments identified that '22 GV70s had a known issue involving injectors that should be covered under warranty, confirming that injector issues are a recognized problem for this model year.

OEM Part Supersession History

• 27310-3L000 → 27310-3N290 — Part consolidation and potential minor design revision for newer models in the Hyundai/Genesis/Kia lineup. The 3.3T engine in the G70 used the -3L000 part, while the newer 3.5T uses the -3N290 part.
  Heads up: While they may appear physically similar, it is critical to use the part number specified for the 3.5T engine (27310-3N290) to ensure correct electrical characteristics and performance.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Electronic Limited-Slip Differential (e-LSD) Noise/Failure 🔴 High — A widely discussed issue, particularly on 2022-2023 Sport Prestige models. Owners report humming or whining noises from the rear, sometimes leading to differential replacement under warranty.
• Sticking Fuel Door Actuator 🟡 Low — A common annoyance where the electronic actuator for the fuel door fails, either preventing the door from opening or from locking. A manual release is located in the trunk.
• Interior Rattles and Creaks 🟡 Low — Owners frequently report various interior rattles, commonly from the sunroof/headliner area, door panels, or overhead 'panic' handles. TSBs exist for some specific noises, like from the sun visor pivot or door handles. (Ref: TSB 21-BD-007G (G70 Sun Visor), TSB 22-01-091G (GV70 Door Handle))
• Premature Fuel Injector Failure 🟠 Medium → Shop Fuel Injector — Beyond causing single-cylinder misfires, there is a pattern of fuel injector failures on the 3.5T engine, sometimes at low mileage, that can lead to recurring check engine lights and rough running.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: An ignition coil is a reasonable part to source used, as long as it's from a verified low-mileage donor vehicle. Since it's an external component that is easy to swap, the financial risk of a premature failure is low.

Donor-vehicle mileage cap: roughly under 40000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check for cracks in the plastic housing or epoxy.
• Inspect the electrical connector pins for corrosion or damage.
• Verify the OEM part number (27310-3N290) is an exact match.
• If possible, get the VIN of the donor car to verify its mileage.

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

• Spark Plugs: These are inexpensive wear items and should always be bought new to ensure performance and longevity.
• Fuel Injectors: Given the documented pattern of GDI injector failures on this platform and the high labor cost for replacement, installing used injectors is not recommended. New OEM injectors provide the best long-term reliability.

Aftermarket brands forum-validated for this vehicle:

• Ignition Coils: NGK, Bosch, Delphi
• Spark Plugs: NGK, Denso

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name ignition coils and fuel injectors from online marketplaces should be avoided. They often have high failure rates and may not meet the precise specifications required for GDI systems.

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 code that often appears alongside P0303 when the engine management system detects misfires across several cylinders.
• P0301 — Misfire code for cylinder 1; used during diagnostic testing when swapping coils from cylinder 3 to confirm a faulty part.
• P0302 — Misfire code for cylinder 2; frequently found stored with P0303 on the 3.5T engine during inspections.
• P219E00 — Cylinder #3 Air-Fuel Ratio Imbalance; a companion code that specifically points to a fuel injector fault in cylinder 3.

Frequently Asked Questions