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

What's Unique About the 2022-2025 Genesis GV70

For the 2.5L Turbo (Theta III) engine, this code is frequently not a hardware problem. Genesis identified an issue with the engine control software that could incorrectly detect misfires, especially on a cold start, causing the vehicle to potentially exceed emission standards. This prompted Service Campaign 914G, a software update to improve misfire detection logic. Therefore, unlike most vehicles where you'd immediately suspect a spark plug or coil, the first step for a 2.5T owner is to check if this free software update has been performed.

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 (can be steady or flashing)
• Rough or vibrating idle
• Engine shaking or hesitating during acceleration
• Noticeable loss of power
• Poor fuel economy
• A smell of fuel from the exhaust
• "Schedule Service" warning appearing on the dashboard display

Most Likely Causes

1. Engine Control Module (ECM) Software Update Needed (2.5T Engine Only) 🔴 High Probability Genesis issued Service Campaign 914G (related to TSB 25-01-051G) specifically to address misfire DTCs (P0300-P0304) on the 2.5L T-GDI engine. The original software was overly sensitive and could falsely detect misfires, particularly at cold start, leading to an erroneous check engine light and potential emissions test failure.
   How to confirm: Contact a Genesis dealership with your VIN. They can verify if Service Campaign 914G is open for your vehicle. This is the mandatory first step for any 2.5T owner seeing this code. Many owners report receiving a notice in the mail or the dealer performing the update during routine service.
   Typical fix: Dealer performs a free software update to the Engine Control Module (ECM). The labor time is typically 0.4 hours (under 30 minutes). Note: Some forum users report that if a hard fault (like a bad coil) is actively present, the dealer may need to replace the hardware before the software update can be applied.
   Est. part cost: $0
2. Faulty Ignition Coil 🟡 Medium Probability Ignition coils are common wear-and-tear items. Once the software issue is ruled out on the 2.5T, this is the next most likely cause. For the 3.5T engine, this is a primary suspect. A Reddit user with a related G70 3.3T reported a P0303 from a failed coil pack at only 19,000 miles.
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1). Clear the codes and drive the vehicle. If the misfire code changes to P0301, the coil is faulty. This is a widely accepted DIY diagnostic method. 🎬 Watch: A step-by-step guide to diagnosing and fixing a P0303 code.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all coils at the same time for preventative maintenance, especially on higher mileage vehicles.
   Est. part cost: $50-$100
3. Worn or Fouled Spark Plug 🟡 Medium Probability Spark plugs are a routine maintenance item with a finite lifespan. A worn plug, or one fouled by carbon or oil deposits, cannot produce a strong enough spark for complete combustion.
   How to confirm: Remove the spark plug from cylinder 3 and inspect it. Look for a worn electrode, white deposits, or black, oily fouling. Compare it to a plug from a healthy cylinder. One owner noted their technician found a 'bllllackkkkk' spark plug when diagnosing a P0303.
   Typical fix: Replace the spark plug in cylinder 3. It is best practice to replace all spark plugs as a set to ensure even performance.
   Est. part cost: $20-$40
4. Faulty Fuel Injector ⚪ Low Probability The GV70 uses a dual-injection system (GDI and MPI). While robust, GDI injectors can become clogged or fail electronically. This has been noted as a potential issue on both the 2.5T and 3.5T engines, sometimes leading to recurring misfire codes even after other repairs. 🎬 See how an intermittent misfire was diagnosed on a GV70.
   How to confirm: This is difficult for a DIYer. A professional would use a scan tool to monitor fuel trims and may perform a balance test. A history of misfire codes (P0302, P0303) combined with lean fuel trim readings on one engine bank can point to injector issues on the 3.5T. A strong smell of fuel in the engine oil is a critical symptom of a leaking GDI injector.
   Typical fix: Replace the faulty fuel injector. This is a more involved and costly job than coils or plugs. One owner experienced recurring misfire codes (P0304, then P0303) that ultimately required two separate dealer visits to replace different fuel injector assemblies.
   Est. part cost: $80-$200

Rare But Worth Checking

• Low-Pressure Fuel Pump Failure: There is a recall (NHTSA 23V630000 / Campaign 022G) for a faulty low-pressure fuel pump impeller on some 2022-2023 models. While this typically causes a sudden loss of power rather than a single-cylinder misfire, it's a known fuel system issue to be aware of.
• Internal Engine Mechanical Issues: Extremely rare on a newer vehicle, but issues like low compression from a valve or piston ring problem could cause a persistent P0303. This would be the last thing to check after all other possibilities are exhausted.
• Loose Solenoid Bolt: In one unusual case on a G70 3.3T, a misfire code was ultimately traced to a loose bolt on a variable force solenoid, demonstrating that mechanical issues, while rare, can be the root cause.

Diagnosis Steps

1. Check for Service Campaigns (2.5T Engine): Before any other step, contact a Genesis dealer with your VIN to see if Service Campaign 914G is open for your vehicle. If it is, schedule the free ECM update. If the check engine light is on, be aware the dealer may need to diagnose an underlying hardware issue before applying the update.
2. Read the Codes: Use an OBD-II scanner to confirm P0303 is the primary code. Note if other codes like P0300 or fuel trim codes are present, and if the check engine light is steady or flashing.
3. Isolate the Ignition System: If the software update has been done or is not applicable (3.5T), swap the ignition coil from cylinder 3 to another cylinder (e.g., cylinder 1).
4. Re-evaluate: Clear the codes and drive the vehicle until the check engine light returns. If the code is now P0301, the ignition coil is bad. If the code remains P0303, the coil is likely good.
5. Inspect the Spark Plug: If the coil is not the issue, remove the spark plug from cylinder 3. Inspect for wear, damage, or fouling. Replace if it is in poor condition or past its service life.
6. Check the Fuel Injector: If the coil and plug are good, the issue may be the fuel injector. Check the oil dipstick for a strong gasoline smell, which indicates a leaking injector. Professional diagnosis is often required for a definitive test.
7. Check for Mechanical Issues: If all else fails, a compression test may be needed to rule out a mechanical engine problem, but this is highly unlikely on a low-mileage vehicle.

Parts You'll Likely Need

• Ignition Coil (2.5T Engine) (OEM #27300-2T000) — This is the most common hardware failure causing a single-cylinder misfire after the ECM software is ruled out. It is used across many Hyundai/Kia/Genesis 2.5T models.
  Trusted brands: Hyundai/Genesis Genuine, NGK, Delphi
  OEM price range: $70-$100
  Aftermarket price range: $40-$70
• Spark Plug (2.5T Engine) (OEM #18875-09085) — Spark plugs are a routine maintenance item and a primary cause of misfires as they wear out. This is the correct OEM part for the 2.5T engine.
  Trusted brands: Hyundai/Genesis Genuine (NGK), NGK
  OEM price range: $25-$40
  Aftermarket price range: $15-$25
• Spark Plug (3.5T Engine) (OEM #18877-09085) — Spark plugs are a routine maintenance item and a primary cause of misfires as they wear out on the V6 engine.
  Trusted brands: Hyundai/Genesis Genuine, NGK
  OEM price range: $25-$40
  Aftermarket price range: $15-$25
• Fuel Injector — A known, though less common, cause of misfires on this platform, sometimes requiring replacement even on low-mileage vehicles. Documented owner experiences show this can be a recurring issue.
  Trusted brands: Hyundai/Genesis Genuine

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) may be stored alongside P0303. This was seen in a case on a 3.5T that was suspected to have injector issues.
• P0301, P0302, P0304 — These codes indicate misfires in other cylinders. Seeing them together with P0303 on a 2.5T strongly points to the ECM software issue covered by Campaign 914G.
• P0171, P0172 — Lean (P0171) or Rich (P0172) condition codes can appear if the misfire is caused by a fuel delivery problem, such as a clogged or leaking fuel injector.

Technical Service Bulletins (TSBs) & Recalls

• 25-01-051G: The technical service bulletin that provides the service procedure for updating the ECM as part of Campaign 914G for misfire DTCs on the 2.5L T-GDI engine.

Platform-Specific Known Issues

• Service Campaign 914G / TSB 25-01-051G: Affects 2022-2025 GV70 models with the 2.5L T-GDI engine. An ECM software update is required to correct misfire detection logic that is overly sensitive, especially during cold starts. This is a no-cost, emissions-related repair performed by Genesis dealers to prevent erroneous P030x codes.

Mechanic-Grade Diagnostic Values

• Short-Term Fuel Trim (STFT) during misfire — expected: Close to 0% at idle.. Failure: Jumping to +25% or higher on the affected bank indicates the ECM is trying to compensate for a lean condition, often caused by a failing MPI injector.
• Downstream O2 Sensor (Sensor 2) Voltage during misfire — expected: A relatively stable voltage, typically above 0.6V.. Failure: Reading near 0 volts indicates a lean condition (excess oxygen), which confirms unburned air/fuel from the misfiring cylinder is reaching the exhaust.
• Crankshaft Position Sensor Signal Waveform — expected: A clean, consistent square wave pattern with no dropouts or glitches when viewed on an oscilloscope.. Failure: A signal that doesn't consistently pull to ground or shows erratic gaps can cause the ECM to misinterpret engine position, leading to intermittent, hard-to-diagnose misfires.

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 MPI injector. A technician can listen for an audible click or use a multimeter to observe the pintle hump on the current waveform to confirm mechanical operation. A weak or absent response points to a faulty injector.

Wiring & Ground Locations

• Passenger Compartment Fuse Box — Located beneath the dashboard on the driver's side.. This panel contains fuses for various interior and control module functions. While a single cylinder misfire is unlikely to be a fuse, checking for any blown fuses related to the ECU or ignition system is a basic step in electrical diagnosis.
• Engine Compartment Fuse Box — Located near the battery in the engine bay.. This main fuse box protects critical engine components, including the ECU, fuel pump, and ignition circuits. A problem here would likely cause multiple codes or a no-start condition, but it's a key location for checking primary power and relays.
• G01 (Engine Compartment Ground) — In the left fender area of the engine compartment.. A poor engine ground can cause a wide range of erratic electrical issues, including weak spark or incorrect sensor readings that could lead to a misfire code. Ensuring this ground connection is clean and tight is a crucial step in advanced electrical troubleshooting.

Real Owner Repair Stories

• Reddit user thelogicalaries (2023 GV70 2.5T Sport Prestige) — Cylinder 3 misfire (P0303) occurred twice, at 9,000 and 12,000 miles. The car had severely limited power, struggling to exceed 40 MPH.
  ❌ Tried (didn't work) The first time, a Hyundai dealer 'moved the coils around' which did not fix the problem.
  ✅ What actually fixed it The second time, a Genesis dealer replaced the fuel pump, and the issue had not returned after another 3,300 miles.
• Reddit user machevara (2023 Genesis G70 (related platform) with 18,000 miles) — Check engine light with code P0303.
  ✅ What actually fixed it The dealer diagnosed and replaced a bad ignition coil pack. The technician also noted the spark plug was 'bllllackkkkk' (very fouled), suggesting it was also compromised.
• Reddit user Malvarado98118 (2023 GV70 Sport Prestige) — Check engine light, recurring issue.
  ❌ Tried (didn't work) The vehicle required three separate dealer visits to resolve the issue.
  ✅ What actually fixed it The final fix was the replacement of two faulty fuel injectors (upper and lower).
• YouTube channel 'Hyundai Tech' (2022 GV70 2.5L) — Intermittent P0301 (Cylinder 1 Misfire) that only occurred on first startup and would not be present when the vehicle arrived at the shop.
  ❌ Tried (didn't work) Swapping the ignition coil and spark plug to different cylinders did not resolve the issue; the misfire code remained on cylinder 1.
  ✅ What actually fixed it Using an oscilloscope, the technician found a glitch in the crankshaft position sensor's signal waveform. Replacing the crankshaft position sensor resolved the intermittent misfire.