P0302 on 2021-2024 Genesis G80: Cylinder 2 Misfire Causes and Fixes

What's Unique About the 2021-2024 Genesis G80

For the 2021-2024 G80 with the 2.5L T-GDI engine, this code has a very specific and documented cause. Genesis issued a Technical Service Bulletin (TSB) because these engines can log misfire codes (including P0302) during a cold start due to a software sensitivity. The official fix is an ECM software update performed by a dealer under Service Campaign 914G. For both the 2.5L and 3.5L GDI (Gasoline Direct Injection) engines, carbon buildup on intake valves can also be a contributing factor to misfires over time, more so than on older port-injected engines. Additionally, some owners of platform-mate vehicles have reported fuel injectors as the cause of persistent misfires after coils and plugs were ruled out.

Diagnostic Flowchart

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

Symptoms You May Notice

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

Most Likely Causes

1. Engine Control Module (ECM) Software Update Needed 🔴 High Probability → Shop Engine Control Module (ECM) Specifically for the 2.5L T-GDI engine, Genesis issued TSB 25-01-051G for misfires (P0300-P0304) during cold starts. The bulletin states that the fix is a software update to the ECM to improve misfire detection logic.
   How to confirm: Contact a Genesis dealership with your VIN to see if Service Campaign 914G (related to TSB 25-01-051G) is open for your vehicle. An owner of a GV70 with the same engine reported the campaign appeared in their app after the code was triggered.
   Typical fix: A Genesis dealer performs an ECM software update. The labor time is estimated at 0.4 hours and is performed free of charge under the campaign.
   Est. part cost: $0 (if covered under campaign/warranty)
2. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a common failure point on most modern engines due to constant exposure to heat and vibration.
   How to confirm: Swap the ignition coil from cylinder 2 with another cylinder (e.g., cylinder 1 or 4). Clear the codes and drive the vehicle. If the code changes to P0301 or P0304, the ignition coil is faulty. This is the standard DIY diagnostic method.
   Typical fix: Replace the faulty ignition coil.
   Est. part cost: $95-$170
3. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug Spark plugs are a regular maintenance item. GDI engines can sometimes cause faster fouling. In some cases, aftermarket spark plugs have been found to cause issues, leading to misfires.
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder 2. Inspect it for wear, carbon tracking, oil fouling, or damage to the electrode or insulator. Compare it to a new plug or a plug from a working cylinder.
   Typical fix: Replace the spark plug. It is recommended to replace all spark plugs at the same time for consistent performance, especially if they are near 🎬 See this walkthrough for replacing spark plugs on the V6. the end of their service life.
   Est. part cost: $25-$40 per plug
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector Gasoline Direct Injection (GDI) systems operate under very high pressure and can be sensitive to fuel quality and deposits. There are reports on forums for the platform-mate GV70 and GV80 where persistent misfires were ultimately traced to faulty fuel injectors, requiring replacement. Hyundai has also issued TSBs for other 2.5L engines regarding internally leaking GDI injectors causing misfires. 🎬 Watch: Real-world example of GDI fuel injector failure and diagnosis.
   How to confirm: This is more difficult for a DIYer. A professional can perform a fuel injector balance test. Swapping injectors is possible but much more involved than swapping coils. If the coil and plug swaps fail to move the misfire from cylinder 2, the injector becomes a more likely suspect.
   Typical fix: Clean or replace the fuel injector for cylinder 2. It is often recommended to replace all injectors as a set, as they tend to wear at a similar rate.
   Est. part cost: $100-$200 per injector

Rare But Worth Checking

• Intake Valve Carbon Buildup: Because GDI engines spray fuel directly into the cylinder, gasoline detergents don't clean the intake valves. Over many miles, carbon can build up, restricting airflow and causing misfires, especially on cold starts. A dealership may recommend a carbon cleaning service if this is suspected.
• Low Engine Compression: Internal engine issues like a bad valve, worn piston rings, or a leaking head gasket can cause a loss of compression in cylinder 2, leading to a misfire. This is a serious mechanical issue requiring professional diagnosis with a compression test.

Diagnosis Steps

1. Read the fault codes with an OBD-II scanner and note any other codes present.
2. If the engine is the 2.5L T-GDI, contact a Genesis dealer with your VIN to check for open campaigns, specifically Service Campaign 914G for TSB 25-01-051G. This should be your first step.
3. If the TSB does not apply or has been completed, locate cylinder 2. On the 2.5L I4, it is the second cylinder from the front. On the 3.5L V6, Bank 1 (cylinders 1, 3, 5) is on the passenger side and Bank 2 (cylinders 2, 4, 6) is on the driver's side. Cylinder 2 is the front-most cylinder on the driver's side.
4. Swap the ignition coil from cylinder 2 with an adjacent, easily accessible cylinder (e.g., cylinder 4).
5. Clear the codes and drive the vehicle until the check engine light returns.
6. Scan the codes again. If the code has moved to the cylinder where you placed the coil (e.g., P0304), the ignition coil is bad and needs to be replaced.
7. If the code remains P0302, the coil is likely good. Swap the spark plug from cylinder 2 with the one from the cylinder you just used for the coil swap.
8. Clear codes and drive again. If the code moves, the spark plug is the issue.
9. If the P0302 code persists after swapping the coil and plug, the problem is more complex. It could be a faulty fuel injector, a wiring issue, or a mechanical compression issue requiring professional diagnosis.

Parts You'll Likely Need

• Ignition Coil (2.5L T-GDI) (OEM #27300-2T000) — This is one of the most common causes of a single-cylinder misfire and is easy to diagnose and replace.
  Trusted brands: Hyundai/Genesis Genuine, Bosch
  OEM price range: $118-$170
  Aftermarket price range: $70-$120
• Ignition Coil (3.5L T-GDI) (OEM #27310-3N290) — A common cause for a single-cylinder misfire on the V6 engine. Note that part numbers can be bank-specific (RH/LH).
  Trusted brands: Hyundai/Genesis Genuine
  OEM price range: $80-$120
  Aftermarket price range: $50-$90
• Spark Plug (2.5L T-GDI) (OEM #18875-09085) — Spark plugs are a maintenance item that wear out over time, leading to a weak spark and misfires.
  Trusted brands: NGK, Denso, Champion
  OEM price range: $28-$40
  Aftermarket price range: $15-$25
• Spark Plug (3.5L T-GDI) (OEM #18877-09085) — A routine maintenance part that can cause misfires when worn or fouled.
  Trusted brands: NGK, Denso
  OEM price range: $29-$40
  Aftermarket price range: $15-$25

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may be stored alongside P0302. This is common with the TSB issue on the 2.5L engine.
• P0301, P0303, P0304 — If other cylinders are also misfiring, their respective codes will appear. This could point to a systemic issue like a vacuum leak, fuel delivery problem, or the ECM software issue on the 2.5L engine.

Technical Service Bulletins (TSBs) & Recalls

• 25-01-051G: ECM SOFTWARE UPDATE – P030X MISFIRE (SERVICE CAMPAIGN 914G). Certain G80 (RG3)... vehicles equipped with Theta III 2.5L T-GDI engines may illuminate the Check Engine Light as a result of misfire DTCs P0300, P0301, P0302, P0303, or P0304 during cold start.

Platform-Specific Known Issues

• TSB 25-01-051G / Service Campaign 914G: Affects 2021-2024 G80 models with the 2.5L T-GDI engine. The manufacturer identified an issue where misfire codes (P0300-P0304) could be triggered during a cold start. The remedy is a free ECM software update provided by Genesis dealers to improve misfire detection logic.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: ~0.660 ohms. Failure: A significantly higher (open circuit) or lower (shorted) reading.
• GDI Fuel Injector Resistance (3.5T) — expected: ~1.9 - 2.2 ohms. Failure: A reading outside of this range, or a significant difference between injectors, can indicate a problem. A technician in a video noted a 0.3 ohm difference between a good and a bad injector.

Hidden / Shadow Codes Worth Checking

• Misfire Counter PID: The Hyundai/Genesis GDS (Global Diagnostic System) dealer scan tool can display live misfire counts for each individual cylinder. This is more precise than a generic P0302 code, as it can show if other cylinders are also experiencing minor, non-code-triggering misfires, helping to isolate a systemic issue versus a single component failure. (see via Requires a dealer-level scan tool like the Hyundai GDS or a high-end professional scanner with equivalent capabilities.)
• Flight Record Data: The GDS VCI tool can access the 'Flight Record' function, which retrieves historical diagnostic data, including past fault codes and freeze-frame data, even if they have been cleared. This is invaluable for diagnosing intermittent misfires that are not present when the vehicle is at the shop. (see via Requires the GDS VCI diagnostic tool and software.)

Scan Tool Commands That Help

• GDS (Global Diagnostic System): DTC Guide / Fault Code Diagnosis Guide — After retrieving a P0302 code, the GDS software provides a step-by-step diagnostic procedure specific to that code for the exact vehicle model. It integrates wiring diagrams and component locations to guide the technician.
• GDS (Global Diagnostic System): Live Data / Current Data — To monitor the misfire counter for cylinder 2 in real-time while the engine is running. A technician can perform a 'power balance' test by observing the counters to confirm if the misfire is active.

Wiring & Ground Locations

• ECM Connector Pin (Ignition) — On a 4-cylinder engine ECM, the control signal for the cylinder #2 ignition coil is often on a specific pin. For example, on one Hyundai ECM, it was pin #40.. If the coil and spark plug are good, a technician must test the control circuit. Knowing the exact pin allows for testing continuity and checking for a signal from the ECM to the coil connector, diagnosing a potential wiring or ECM driver issue.
• ECM Connector Pin (Injector) — On a Hyundai ECM, the control output for the cylinder #2 fuel injector was located at pin #8.. When a misfire is not caused by the ignition system, the fuel injector circuit is the next logical step. This pin is the starting point for diagnosing a wiring fault or a faulty injector driver in the ECM.

Real Owner Repair Stories

• YouTube user 'Importech', a professional technician (2021 Genesis GV80 3.5T) — Intermittent check engine light, history code for cylinder 2 misfire, then later a code for cylinder 4 misfire.
  ❌ Tried (didn't work) The misfire was very intermittent and would not occur during shop testing. The technician initially suspected an open circuit in a GDI injector, which was a previous issue on the same vehicle.
  ✅ What actually fixed it The technician swapped the ignition coil from cylinder 2 to cylinder 4. After a week of driving, the misfire code returned as a P0304 (Cylinder 4 Misfire). This confirmed the ignition coil was faulty, and it was replaced, solving the issue.
• YouTube user 'Importech', a professional technician (Genesis GV80 V6 Turbo (year not specified)) — Persistent, multiple misfire codes, including on cylinders 2 and 4, after previous repairs.
  ❌ Tried (didn't work) Pressure testing the cooling system (no leaks found), swapping coils and plugs.
  ✅ What actually fixed it The technician measured the resistance of the GDI fuel injectors and found a variance between them. After replacing the injector on the persistently misfiring cylinder (#4) and all spark plugs, the misfires were resolved. The video highlights that GDI injectors were the ultimate point of failure.
• Reddit user in r/GenesisMotors (2024 GV80 3.5T Prestige with ~4,000 miles) — Check engine light and engine misfire.
  ❌ Tried (didn't work) Dealer reset the code, but it returned. A 'full diagnostic' by the dealer found nothing. The dealer then replaced a fuel injector, but the check engine light came back on again (for a different 'knock sensor' issue).
  ✅ What actually fixed it The issue was not resolved by the time of the post. The owner was initiating a vehicle repurchase (buyback) process with Genesis corporate due to the persistent, unfixable problems. This story highlights that on the 3.5T, misfires can be complex and sometimes lead to injector replacement, which may not even be the final fix.

OEM Part Supersession History

• 27300-2GGA0 → 27300-2T000 (for 2.5T) — Part number 27300-2GGA0 is for the older 2.0L/2.4L engines. While it may appear similar, the correct part for the 2.5L Turbo in the G80 is 27300-2T000. Using the wrong coil can cause performance issues.
  Heads up: The coils are not interchangeable between the different engine families (2.0L, 2.5L non-turbo, 2.5L turbo). The part number must be matched to the specific engine.