P0304 on 2022-2025 Genesis GV70: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2022-2025 Genesis GV70

The 2022-2025 Genesis GV70, particularly with the 2.5L Turbo "Theta III" engine, has a well-documented issue where misfire codes (P0300-P0304) can be triggered by overly sensitive ECM logic, especially during a cold start. Genesis has issued Technical Service Bulletin 25-01-051G and a corresponding Service Campaign (914G) to fix this with a free ECM software update, making a trip to the dealer the most important first diagnostic step for 2.5T owners. Additionally, both the 2.5T and 3.5T engines use Gasoline Direct Injection (GDI), which can make them susceptible to issues like carbon buildup on intake valves (a potential cause of misfires on the 3.5T) and specific fuel injector faults that are less common on traditional port-injection-only engines.

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 engine idle
• Noticeable loss of power and acceleration
• Engine hesitation or stumbling
• Reduced fuel economy
• Smell of unburned fuel from the exhaust
• Vehicle shudders when stationary

Most Likely Causes

1. Engine Control Module (ECM) Software Update Needed (2.5L Engine Only) 🔴 High Probability → Shop Engine Control Module (ECM) Genesis issued TSB 25-01-051G and Service Campaign 914G specifically to address misfire codes P0300-P0304 on 2022-2025 GV70s with the 2.5L T-GDI engine. The original software logic was too sensitive and could falsely detect misfires during cold starts. This campaign was also initiated because the California Air Resources Board determined the issue could cause vehicles to exceed emission standards.
   How to confirm: Contact a Genesis dealership and provide your vehicle's VIN. They can confirm if TSB 25-01-051G or Service Campaign 914G is open and applicable for your vehicle. Some owners may have received a notice that their vehicle is NOT affected, as the software was revised during production.
   Typical fix: A Genesis dealer will update the ECM software with improved logic. This is performed free of charge under the service campaign and typically takes less than an hour.
   Est. part cost: $0
2. Faulty Ignition Coil 🟡 Medium Probability → Shop Ignition Coil Ignition coils are a common wear item on modern turbocharged engines due to high heat and vibration. A coil failure leads to a weak or non-existent spark, causing a misfire. This is a primary suspect for the 3.5T engine or for a 2.5T engine after the ECM update has been performed.
   How to confirm: The easiest way is to perform a 'coil swap'. Move the ignition coil from cylinder 4 to another cylinder (e.g., cylinder 1). Clear the codes and run the engine. If the code changes to P0301 (Cylinder 1 Misfire), the coil is bad.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all coils on the affected bank (or all of them) at the same time, especially on higher mileage vehicles, to prevent future failures.
   Est. part cost: $40-$80
3. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug
   How to confirm: Remove the spark plug from cylinder 4 and inspect it. Look for a worn electrode, heavy carbon deposits, oil fouling, or cracks in the porcelain. Compare it to a plug from a working cylinder.
   Typical fix: Replace the spark plug. It is best practice to replace all spark plugs as a set to ensure even performance and avoid repeat labor.
   Est. part cost: $15-$30 per plug
4. Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector The GV70 uses both GDI (direct) and MPI (port) injectors. A failure or clog in the injector serving cylinder 4 can cause a lean misfire. A technician on YouTube documented a P0304 on a 2022 GV70 2.5L being caused by a failed MPI injector, which was diagnosed by observing a lean condition and abnormal injector waveforms. 🎬 Watch a technician diagnose this specific P0304 injector failure. Some owners on forums have also suspected injector or fuel pump issues as the root cause of their misfires.
   How to confirm: This is an advanced diagnosis. After ruling out spark, a mechanic can monitor fuel trims for cylinder 4. High positive fuel trim suggests the ECM is trying to compensate for a lean condition, pointing to a clogged or failing injector. Further tests include checking injector resistance or performing a flow test.
   Typical fix: Replace the faulty fuel injector. The MPI injectors are more accessible than the GDI injectors, which are located under the intake manifold.
   Est. part cost: $70-$200

Rare But Worth Checking

• Carbon Buildup on Intake Valves (Especially 3.5T): Because GDI engines inject fuel directly into the cylinder, gasoline detergents don't clean the back of the intake valves. Over time, oil vapor from the PCV system can bake onto the valves, restricting airflow and causing misfires, rough idle, and hesitation. This is more likely on vehicles over 60,000 miles. A DIY chemical cleaning or professional walnut blasting service can resolve this.
• Faulty Crankshaft Position Sensor: A failing crankshaft position sensor can send erratic signals to the ECM, especially during startup. This can cause the ECM to incorrectly identify a misfire on a specific cylinder. One technician documented a case on a GV70 2.5L where an intermittent cylinder 1 misfire was ultimately traced to a bad crankshaft position sensor that was creating false signals on the waveform.
🎬 See how a bad crankshaft sensor causes intermittent misfires.
• Low Engine Compression: While rare on a newer vehicle, internal engine issues like a leaking valve, damaged piston, or head gasket failure can cause a permanent misfire. This should only be investigated with a compression test after all ignition and fuel-related causes have been ruled out.
• Vacuum Leak: A vacuum leak near the intake manifold runner for cylinder 4 could lean out the air/fuel mixture and cause a misfire, though this would likely be accompanied by other lean codes and affect idle more broadly.

Diagnosis Steps

1. (2.5L Engine Only) Check for Service Campaign 914G: Before any other step, contact a Genesis dealer with your VIN to see if TSB 25-01-051G or Service Campaign 914G is active for your vehicle. If so, have the dealer perform the free ECM update.
2. Read Freeze Frame & Misfire Data: Use an OBD-II scanner to look at the freeze frame data. This shows engine conditions (RPM, temp, load) when the code was set. Also, use the scanner's live data function to view the misfire counter for each cylinder to confirm the misfire is isolated to cylinder 4.
3. Inspect Ignition System: Check the wiring and connector for the cylinder 4 ignition coil for any damage, corrosion, or loose connections.
4. Perform Coil Swap: Swap the ignition coil from cylinder 4 with one from another cylinder (e.g., cylinder 2). Clear the codes and drive the vehicle. If the code returns as P0302, the ignition coil is the problem. This is the most effective way to isolate a bad coil.
🎬 Watch this video for a step-by-step ignition coil replacement.
5. Inspect Spark Plug: If the misfire remains on cylinder 4, remove and inspect the spark plug for wear, damage, or fouling. A heavily fouled or worn plug is a likely cause. Replace if necessary.
6. Check Fuel System: If spark is confirmed good, the issue may be fuel-related. A professional may need to test the cylinder 4 fuel injector's circuit and function, possibly by observing fuel trims or injector waveforms with an oscilloscope.
7. Check for Mechanical Issues: If all else fails, perform a compression test on cylinder 4 to check for mechanical engine problems like poor valve seating or piston ring issues. A leak-down test can further pinpoint the source of compression loss.

Parts You'll Likely Need

• Engine Control Module (ECM) Software Update (OEM #Campaign 914G) — For the 2.5L engine, this is the most common fix mandated by Genesis to correct misfire detection logic, especially for cold-start misfires.
  Trusted brands: Genesis OEM Service
  OEM price range: $0
  Aftermarket price range: N/A
• Ignition Coil (2.5T) (OEM #27301-2TBA0) — A common failure point for misfires. The OEM part number for the 2.5T ignition coil is sometimes listed as 27300-2T000, but 27301-2TBA0 is also associated with this engine family. Always confirm with a dealer using your VIN.
  Trusted brands: Hyundai/Genesis OEM
  OEM price range: $40-$80
  Aftermarket price range: $25-$60
• Spark Plug — Spark plugs are a routine maintenance item and a common cause of misfires. A fouled or worn plug on cylinder 4 will prevent a proper spark.
  Trusted brands: NGK, Denso
  OEM price range: $20-$40
  Aftermarket price range: $15-$30
• MPI Fuel Injector (2.5T) — In documented cases, the Multi-Port Injector (MPI) for cylinder 4 has failed, causing a lean misfire that persists after swapping ignition components.
  Trusted brands: Hyundai/Genesis OEM
  OEM price range: $70-$150
  Aftermarket price range: $50-$100

Related Codes That Often Appear With This One

• P0300 — This code for 'Random/Multiple Cylinder Misfire' often appears alongside a specific cylinder code like P0304 if the misfire is intermittent or affecting other cylinders as well. The TSB for the 2.5L engine covers P0300 in addition to P0301-P0304.
• P0171 or P0174 — System Too Lean (Bank 1 or 2). These codes might appear if the misfire is caused by a vacuum leak or a clogged fuel injector that is not providing enough fuel to the cylinder(s).

Technical Service Bulletins (TSBs) & Recalls

• 25-01-051G: Addresses Check Engine Light illumination for misfire DTCs P0300-P0304 on 2.5L T-GDI engines by providing an ECM software update. This is the basis for Service Campaign 914G.

Platform-Specific Known Issues

• TSB 25-01-051G / Service Campaign 914G: Affects 2022-2025 models with the 2.5L T-GDI engine. The ECM may incorrectly detect misfires (P0300-P0304) during a cold start. The fix is a dealer-installed software update, which is free of charge for affected VINs.
• Owner Frustration with Diagnosis: Some owners on forums have expressed frustration with dealers, who sometimes blame fuel quality before acknowledging the TSB or investigating other causes.

Mechanic-Grade Diagnostic Values

• Short-Term or Long-Term Fuel Trim (STFT/LTFT) for Bank 1 — expected: Typically between -5% and +5% at idle.. Failure: A sustained positive fuel trim of +25% or higher on the bank with the misfiring cylinder strongly suggests a lean condition, such as a clogged or failed fuel injector.
• Secondary Ignition Waveform (Oscilloscope) — expected: A consistent waveform pattern across all cylinders.. Failure: On a cylinder with a lean misfire due to a bad injector, the end of the waveform (the 'tail') may go high up instead of sloping down, indicating a lean ignition event.

Scan Tool Commands That Help

• Genesis GDS (Global Diagnostic System): Current Data / Live Data Analysis — The official dealer tool can be used to monitor the misfire counter for each specific cylinder in real-time, view fuel trims, and access guided diagnostic procedures from Genesis service information.
• Genesis GDS (Global Diagnostic System): ECU Update — This function is required to perform the software update outlined in TSB 25-01-051G for the 2.5L engine to correct the misfire detection logic.
• Advanced Scan Tool (e.g., Autel, Snap-on, GDS): Injector Activation Test — After ruling out ignition issues, a bidirectional scan tool can be used to command the fuel injector for cylinder 4 to fire. This helps confirm if the injector is mechanically functioning and if the control circuit is intact.

Wiring & Ground Locations

• Battery Location — In the cargo area, underneath the spare tire.. A poor battery state of charge or bad connections can cause widespread electrical issues. While jump-start posts are available under the hood, knowing the actual battery location is critical for testing the battery itself or for a full electrical system reset.
• Under-hood Jump Start Posts — The positive (+) terminal is under a red plastic cover in the engine bay fuse box. The negative (-) post is typically an unpainted stud on the chassis or engine block nearby.. Provides a convenient point for checking system voltage or jump-starting the vehicle without accessing the rear-mounted battery. Stable voltage is essential for proper ECM and ignition system operation.

Real Owner Repair Stories

• YouTube channel 'Hyundai Tech' (2022 Genesis GV70 2.5L Turbo) — Check engine light on and engine shaking (misfire). Code P0304 was present.
  ❌ Tried (didn't work) Swapping the ignition coil and spark plug from cylinder 4 to cylinder 1. The misfire code remained on cylinder 4 (P0304).
  ✅ What actually fixed it The technician diagnosed a lean condition using fuel trim data (+29%) and an oscilloscope. The final diagnosis was a failed MPI (Multi-Port Injection) fuel injector for cylinder 4. The repair involved replacing the MPI injector.

OEM Part Supersession History

• 27301-2B010 → 27301-2B120 — Part number evolution for ignition coils within the Hyundai/Kia family. While 27301-2TBA0 is often cited for the 2.5T, other numbers like these may appear in parts catalogs for related engines. Compatibility must be verified by VIN.
  Heads up: Using an incorrect ignition coil, even if it physically fits, can lead to improper dwell time, weak spark, and persistent misfires. Always verify the part number with a Genesis dealer.

Model Year Variations Within This Range

• 2022-2025: The ECM software for the 2.5L T-GDI engine was revised during the production run to correct overly sensitive misfire detection. As a result, not all vehicles within this year range will have the faulty software. A dealer must check the VIN to determine if Service Campaign 914G is applicable.