2021-2023 Hyundai Misfire DTCs TSB 26-FL-001H

Hyundai Technical Service Bulletin (TSB) 26-FL-001H, issued in January 2026, addresses a common issue affecting certain 2021-2023 Hyundai vehicles equipped with the 2.5L GDI Theta III (non-Turbo) engine. This bulletin supersedes previous TSB 25-FL-001H, updating warranty operation times for the repair.

The TSB details how internally leaking GDI fuel injectors can lead to engine misfire diagnostic trouble codes (DTCs). This internal leakage is often a result of filter breakage within the injector itself. Owners experiencing symptoms related to engine misfires, such as rough idling or reduced performance, may find this information relevant.

Symptoms

Owners of affected Hyundai models may experience engine misfires. These misfires are typically indicated by the illumination of the Check Engine Light and the storage of specific Diagnostic Trouble Codes (DTCs) in the vehicle's engine control module.

Fault Codes / DTCs

The following misfire DTCs are associated with internally leaking GDI fuel injectors in the affected vehicles:

• P0300: Random/Multiple Cylinder Misfire Detected
• P0301: Cylinder 1 Misfire Detected
• P0302: Cylinder 2 Misfire Detected
• P0303: Cylinder 3 Misfire Detected
• P0304: Cylinder 4 Misfire Detected

Important Warnings for Owners

Owners should be aware of specific conditions and requirements related to this service action:

• "This field action requires justification in the form of a customer concern, and a confirmed case for the related symptom outlined in the TSB, prior to any repair work. If justification requirements are not met, any submitted claims are subject to debit."
• "If none of these DTCs are found, and/or vehicle is NOT within the Applicable Vehicle range, then this TSB does NOT apply. Follow the normal diagnostic process."
• "Claim is subject to debit if the part is not returned." (Referring to incident parts subject to callback).
• "NOTE: If the STUI camera function is NOT used, write the last 6 digits of the VIN and date of repair on a piece of paper to include in the photo." (This is a dealer-facing instruction for documentation).

Diagnosis and Trigger Conditions

Diagnosis for this issue involves performing a fault code search for the specified misfire DTCs (P0300, P0301, P0302, P0303, P0304). If one or more of these codes are present and the vehicle falls within the applicable range for TSB 26-FL-001H, the GDI fuel injector replacement procedure should be followed. If no misfire DTCs are found or the vehicle is outside the applicable range, this TSB does not apply, and normal diagnostic procedures should be followed.

Repair Procedure Summary

The repair outlined in TSB 26-FL-001H involves replacing all four GDI fuel injectors. The procedure is comprehensive and requires careful attention to detail:

1. Preparation: Release residual pressure in the fuel line, record customer radio presets, and disconnect the negative battery cable.
2. Disassembly: Remove the engine cover, ignition coil connectors, ignition coil foam, high pressure pump foam, and the air cleaner assembly.
3. Fuel System Access: Remove the high-pressure fuel pipe bracket bolts and flange nut. Then, remove the intake manifold and injector foam.
4. Injector Removal: Disconnect the injector and rail sensor connectors. Remove the high pressure fuel pipe flange nut and bolts, then detach the delivery pipe and injector assembly from the fuel rail.
5. Installation: Clean each cylinder head hole to remove carbon deposits and foreign materials. Install the new GDI fuel injectors and associated components in the reverse order of removal, ensuring proper torque specifications are met. Special care must be taken not to deform the new high-pressure fuel pipe, damage the injector tip, or apply oil/grease to the combustion seal.
6. Final Steps: Reinstall all remaining parts, reset radio presets, reconnect the battery, and start the engine to confirm proper operation.

Required Tools or Parts

To perform the GDI fuel injector replacement, a specific kit and a special service tool are required:

• Kit: 35399-2S133QQH (contains all necessary components)
• Individual Parts (included in kit):
  • Fuel Injector – GDI: 35310-2S000 (Qty: 4)
  • Clip – Fuel Injector: 35309-04AA0 (Qty: 4)
  • Pipe - High Pressure: 35305-2S000 (Qty: 1)
  • Gasket - Port: 28411-2S010 (Qty: 3)
  • Gasket – Port FKM: 28411-2S020 (Qty: 1)
  • Gasket - Throttle Body: 28411-2S000 (Qty: 1)
  • Gasket – EGR Pipe: 28493-2S000 (Qty: 1)
  • Gasket – Oil Filter Housing: 26333-2S000 (Qty: 2)
• Special Service Tool (SST): Torque Wrench Socket 09314-L1100 (used for High Pressure Fuel Pipe Removal).

Owner Action

If your 2021-2023 Hyundai Santa Fe, Santa Cruz, Sonata, or Tucson is experiencing engine misfire symptoms or has illuminated the Check Engine Light with DTCs P0300-P0304, it is recommended to contact an authorized Hyundai dealership. The dealership will be able to diagnose the issue according to TSB 26-FL-001H and perform the necessary GDI fuel injector replacement. This repair is typically covered under the New Vehicle Limited Warranty, provided the justification requirements are met.