P0304 on 2021-2024 Genesis GV80: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2021-2024 Genesis GV80

For the 2021-2024 GV80 with the 2.5L Turbo engine, this code is very often not a hardware problem. Genesis issued a Technical Service Bulletin (TSB 25-01-051G) acknowledging that P030x misfire codes can be falsely triggered on cold starts due to overly sensitive ECM logic. Before you or your mechanic replace any parts on a 2.5T model, the first step should always be to check if the free ECM software update (Service Campaign 914G) has been performed. For both engines, the dual-injection system (GDI and MPI) adds complexity; a misfire could be related to either the direct injector or the port injector.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on or flashing
• Rough or shaking idle
• Noticeable loss of power and sluggish acceleration
• Engine hesitates or stumbles
• Reduced fuel economy
• Smell of unburned gasoline from the exhaust
• Engine vibration that is more noticeable under load or during acceleration

Most Likely Causes

1. Engine Control Module (ECM) Software Update Needed 🔴 High Probability → Shop Engine Control Module (ECM) Applies only to the 2.5L T-GDI engine. Genesis issued TSB 25-01-051G because the original ECM logic was too sensitive, causing false misfire codes (P0300-P0304) during cold starts. This was determined to cause the vehicle to exceed emissions standards.
   How to confirm: Contact a Genesis dealer with your VIN. They can verify if Service Campaign 914G is open for your vehicle. You can also check for open recalls on the Genesis website.
   Typical fix: The dealer will update the ECM software. This is a service campaign item and should be performed at no cost to the owner. The repair takes approximately 0.4 labor hours.
   Est. part cost: $0
2. Faulty Ignition Coil 🟡 Medium Probability → Shop Ignition Coil Coil-on-plug ignition coils are a common failure point on most modern engines due to constant exposure to high heat and vibration. Failure leads to a lack of spark in the cylinder. This has been documented by technicians working on the 3.5L V6 as well.
   How to confirm: Swap the ignition coil from cylinder 4 with another cylinder (e.g., cylinder 2). Clear the codes and drive. If the code returns as P0302, the coil is confirmed bad. For the 2.5L I4, cylinders are numbered 1-2-3-4 from front to back. For the 3.5L V6, cylinder 4 is on the driver's side, second from the front.
   Typical fix: Replace the faulty ignition coil. It is a simple, single-bolt replacement accessible after removing the engine cover. 🎬 See this walkthrough on how to replace an ignition coil.
   Est. part cost: $50-$100
3. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder 4. Inspect it for wear (rounded electrode), carbon fouling, oil contamination, or incorrect gap. A worn plug cannot produce a strong enough spark.
   Typical fix: Replace the spark plug in cylinder 4. It is best practice to replace all spark plugs as a set if they are near the end of their service life (typically recommended around 40,000-60,000 miles). 🎬 Watch: How to replace spark plugs on the Genesis V6 engine.
   Est. part cost: $15-$40 per plug
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector While less common than ignition issues, owners of platform mates with the 2.5T engine have reported clogged fuel injectors causing misfires at very low mileage (e.g., 13,000 miles). The engine's dual injection system means either the GDI (direct) or MPI (port) injector could be at fault.
   How to confirm: This is more complex. A professional can perform a fuel injector balance test. A DIY method involves listening to the injector with a mechanic's stethoscope to ensure it's clicking. A technician diagnosed a faulty MPI injector on a 2.5T GV70 after ruling out ignition components.
   Typical fix: Replace the faulty fuel injector. The MPI injectors are easier to access than the GDI injectors, which are located under the intake manifold.
   Est. part cost: $100-$250

Rare But Worth Checking

• Internal Engine Mechanical Failure: On the 2.5L Smartstream engine family, there have been some reports of issues like excessive oil consumption or piston ring failure that can lead to a loss of compression and misfires. This is a worst-case scenario and should only be considered after all ignition and fuel causes are ruled out via a compression test.
• Leaking Valve Cover Gasket: → Shop Engine Valve Cover While not a direct cause, a leaking valve cover gasket can allow oil to pool in the spark plug tube. This oil can saturate the ignition coil boot and cause the coil to fail, leading to a misfire. When replacing a coil, it's crucial to inspect the spark plug tube for oil.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0304 and check for any other codes, especially P0300.
2. (2.5L Engine Only): Contact a Genesis dealer with your VIN to check if TSB 25-01-051G (Service Campaign 914G) is open for your vehicle. If it is, have the dealer perform the free ECM update. This is the most probable fix.
3. If the TSB does not apply or has been completed, perform an 'ignition coil swap'. Label and move the coil from cylinder 4 to cylinder 2. Clear the codes. If the misfire code changes to P0302, the coil is bad and needs replacement.
4. If the code remains P0304 after the coil swap, inspect the spark plug in cylinder 4. Look for wear, damage, or fouling. Also inspect the spark plug tube for any signs of oil from a leaking valve cover gasket. Replace the plug if necessary.
5. If the coil and plug are good, the issue may be with the fuel injector. A technician on a 2022 GV70 with a P0304 traced the issue to a faulty MPI (port) fuel injector after ignition components checked out.
🎬 Watch: A technician diagnoses a P0304 code on this engine platform.
6. If ignition and fuel delivery seem okay, a mechanical issue is possible. Perform a compression test to check for low compression in cylinder 4, which could indicate a serious internal engine problem like a bad valve or piston ring issue.

Parts You'll Likely Need

• Ignition Coil (2.5L I4) (OEM #27300-2T000) — This is the most common hardware failure causing a single-cylinder misfire on the 2.5L Turbo engine.
  Trusted brands: Hyundai/Genesis OE, Bosch, NGK
  OEM price range: $70-$120
  Aftermarket price range: $45-$80
• Ignition Coil (3.5L V6) (OEM #27310-3N290) — A common hardware failure for single-cylinder misfires on the 3.5L Twin-Turbo V6. Note that this is for the right-hand bank (cylinders 2, 4, 6).
  Trusted brands: Hyundai/Genesis OE
  OEM price range: $80-$130
  Aftermarket price range: $50-$90
• Spark Plug (2.5L I4 & 3.5L V6) (OEM #18875-09085) — Spark plugs are a routine maintenance item and can wear out, causing a weak or inconsistent spark. This part number appears to be used for both engines.
  Trusted brands: NGK, Denso, Hyundai OE
  OEM price range: $25-$40
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0300 — P0300 means 'Random/Multiple Cylinder Misfire'. It often appears with P0304 if the misfire is intermittent or affecting other cylinders as well, which is a key symptom of the 2.5L T-GDI software issue.
• P0301, P0302, P0303 — These codes indicate misfires in cylinders 1, 2, and 3, respectively. Seeing them alongside P0304 points to a problem affecting the entire engine, such as the ECM software issue, a vacuum leak, or low fuel pressure.

Technical Service Bulletins (TSBs) & Recalls

• 25-01-051G / Service Campaign 914G: Addresses misfire DTCs P0300-P0304 on 2.5L T-GDI engines during cold start by providing an ECM software update. The TSB notes this is to correct an issue causing the vehicle to exceed emissions standards.

Platform-Specific Known Issues

• A known issue for 2021-2024 models with the 2.5L T-GDI engine is the illumination of the check engine light with misfire DTCs (P0300-P0304) during a cold start. This is addressed by Genesis TSB 25-01-051G, which provides an ECM software update.

Mechanic-Grade Diagnostic Values

• GDI Fuel Injector Resistance (3.5L V6) — expected: ~2.1 - 2.2 Ohms. Failure: A reading in the kilo-ohm (kΩ) range or 'O.L.' (Open Loop) indicates an electrically failed injector.

Hidden / Shadow Codes Worth Checking

• Mode $06 Misfire Data: This is not a 'code' but a diagnostic function. The ECU tracks misfires on each cylinder even if the count isn't high enough to trigger a Check Engine Light. Accessing Mode $06 with an advanced scan tool allows a technician to see the raw misfire count for each cylinder during the current and previous drive cycles. (see via Requires a professional-grade scan tool with Mode $06 viewing capabilities. The specific monitor ID for misfire data is typically designated as '$A2' through '$AB' for cylinders 1-10.)

Scan Tool Commands That Help

• Genesis GDS (or equivalent professional scanner): Injector Kill Test / Power Balance Test — This function is used when a fuel injector is suspected as the cause of a misfire. The tool commands the ECU to shut off one injector at a time while the engine is running. If disabling an injector causes no change in engine RPM or smoothness, that injector was not contributing, confirming it is faulty.

Wiring & Ground Locations

• Engine Compartment Fuse & Relay Box — Located under the hood, typically on the driver's side.. This box contains the primary fuses and relays for the Engine Control Module (ECU), ignition coils, and fuel injectors. A faulty relay or poor connection in this box could cause issues that mimic a failed component.

Real Owner Repair Stories

• YouTube - 'Hyundai Tech' (2022 Genesis GV70 2.5T) — Check engine light on and engine shaking, code P0304.
  ❌ Tried (didn't work) Swapping ignition coil from cylinder 4 to cylinder 1., Swapping spark plug from cylinder 4 to cylinder 1.
  ✅ What actually fixed it Diagnosis with a lab scope on the injector waveform indicated a problem. The technician identified the MPI (Multi-Port Injection) fuel injector for cylinder 4 as faulty and ordered a replacement. This highlights that the less common port injector can be the cause, not just the GDI injector.
• YouTube - 'GENESIS GV80 V6 TURBO MULTIPLE GDI INJECTORS FAILURE' (2021+ Genesis GV80 3.5T V6) — Persistent misfires on cylinders 2 and 4 (P0302, P0304).
  ❌ Tried (didn't work) Initial diagnosis was complicated by the previous discovery of coolant inside a cylinder, suggesting a head gasket leak.
  ✅ What actually fixed it The technician performed a resistance test on the GDI injectors for the affected bank. He found the cylinder 2 injector had a resistance of 9.7 kOhms (a near-open circuit), while the other injectors measured a healthy ~2.1 Ohms. Replacing the faulty GDI injector resolved the misfire.

OEM Part Supersession History

• 27310-3N290 →
  Heads up: This is the ignition coil for the 3.5L V6. Parts diagrams designate it as 'COIL-IGNITION,RH' for the Right-Hand bank of the engine. On the transverse V6, the RH bank contains cylinders 2, 4, and 6, making this the correct part for a P0304 code.