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Service bulletin 21-01-051H

A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.

The communication, as NHTSA indexes it (as of 2026-10-19)
TypeService bulletin
NHTSA id10199099
Published by NHTSA2021-07-09
Manufacturer's number21-01-051H
Manufacturer's date2021-06-22
NHTSA componentENGINE AND ENGINE COOLING

NHTSA's summary

This bulletin provides information related to an Electronic Control Module (ECM) software update which revises the OBD Air Fuel Ratio Imbalance (AFRI) monitor function frequency and cylinder imbalance diagnosis logic.

The document

The document is the manufacturer's. This site does not hold it. NHTSA files a document at one of these two addresses; we have not asked NHTSA which.

Components

Engine

Vehicles listed
HYUNDAI SONATA2020, 2021

Listing a model year does not mean every vehicle of it is concerned: the document says which.

Other bulletins for the same vehicles and component
26-EM-016H TSB2026-10-14. Service bulletin. Some vehicles equipped with internal combustion engines may exhibit higher-than-expected engine oil consumption. This bulletin outlines the combustion chamber cleaning procedure for vehicles diagnosed with this condition. All internal combustion engines consume some engine oil during normal operation, depending on driving conditions and mileage, and this procedure should only be performed when deemed necessary based on inspection and diagnosis of the vehicle as outlined in TSB 26-EM-015H, Engine Oil Consumption – Inspection & Repair Guidelines, or the latest revision.
26-EM-015H TSB2026-10-13. Service bulletin. Certain vehicles equipped with internal combustion engines may exhibit higher-than-expected engine oil consumption. This bulletin provides the inspection and repair procedures for vehicles exhibiting this condition. All internal combustion engines consume engine oil as part of normal engine operation. Oil consumption rates may vary based on mileage, operating conditions, driving habits, and maintenance history. Hyundai recommends following the prescribed maintenance schedule and periodically checking the engine oil level using the dipstick to maintain proper engine oil level.
26-EE-003H TSB2026-04-21. Service bulletin. Some vehicles may exhibit difficulty starting in cold weather. This bulletin provides the procedure to perform an inspection on the starter magnetic switch for potential freezing and, if necessary, replace the starter magnetic switch (solenoid) assembly.
26-EM-003H TSB2026-02-10. Service bulletin. Some Sonata (DN8, DN8A) vehicles may have DTCs P218100, P2181F0, and/or P2181F1 (Cooling System Performance) set in the Engine Control Module, resulting in an illuminated Check Engine warning lamp. Follow the procedure in this TSB to replace the Integrated Thermal Management (ITM) module and update both the Engine Control Module (ECM) and Transmission Control Module (TCM) if applicable. Follow the flowchart in this TSB to update the appropriate modules.
25-EM-007H TSB2026-01-06. Service bulletin. Some Elantra (CN7, CN7A), Kona (OS, SX2), and Sonata Hybrid (DN8 HEV) vehicles equipped with 2.0L engines may illuminate a warning lamp for DTC P218100 (Cooling System Performance) related to the Integrated Thermal-Management Module (ITM). Follow the service procedure in this bulletin to install a spring onto the thermostat within the ITM, in order to prevent premature opening, and perform an ECU software update on affected vehicles.
25-EE-002H2025-05-02. Service bulletin. Certain Sonata (DN8) and Sonata (DN8A) vehicles may experience issues with the air conditioning due to damaged wiring in the engine room junction box. This bulletin provides instructions to replace the multi-fuse, reroute the damaged wiring using the blower wiring kit, and replace the fuse label.
24-EM-001H2024-08-07. Service bulletin. Certain 20-22MY Sonata (DN8a), 21-23MY Santa Fe (TMa), and 22-23MY Tucson (NX4a) vehicles may experience a warning lamp illumination for a diagnostic trouble code P2181 that is related to the Integrated Thermal Management Module (ITM). Follow the service procedure outlined in this bulletin to replace the ITM.
24-FL-002H2024-03-05. Service bulletin. This bulletin provides the procedure to update the Engine Control Module (ECM) and/or the Transmission Control Module (TCM) for 2020-2023MY Sonata (DN8/DN8a) vehicles to improve operation of the Idle Stop and Go (ISG) system. Under certain circumstances the vehicle may not restart after the ISG system has engaged and requires a manual restart due to the lack of intake manifold pressure recovery.
23-01-093H2024-02-05. Service bulletin. This bulletin provides the procedure to update the Hybrid Control Unit (HCU) and Dual Automatic Temperature Control (DATC) software to help improve coolant flow to the Exhaust Heat Recovery System (EHRS).
23-EM-009H2023-12-22. Service bulletin. Certain 2020-2023MY Sonata Hybrid (DN8 HEV) vehicles may exhibit coolant leakage, engine overheating, and white smoke from the exhaust due to an internal leak at the Exhaust Heat Recovery System (EHRS) portion of the center muffler assembly. Follow the procedure outlined in this bulletin to repair this condition after confirming EHRS is leaking internally.