Service bulletin 21-AT-001H

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)
Type	Service bulletin
NHTSA id	10186820
Published by NHTSA	2021-02-06
Manufacturer's number	21-AT-001H
Manufacturer's date	2021-01-14
NHTSA component	POWER TRAIN

NHTSA's summary

This bulletin provides the procedure to update the TCU for a rough idle in Drive with Neutral Control enabled. The rough idle may occur only at a stop in Drive with the A/C off and the ATF temperature between 158~210°F (70~99°C). This update also reduces vibration when the brake is released during Neutral Control operation and the accelerator pedal is depressed.

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

Transmission and driveline

Vehicles listed
HYUNDAI SONATA	2018, 2019

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

Recalls for the same vehicles and component
2018135	2018-03-16. Powertrain

A recall listed here may apply to some of the same vehicles. Only the manufacturer can say whether it applies to one vehicle.

Other bulletins for the same vehicles and component
24-AT-002H	2024-04-16. Service bulletin. This TSB provides a procedure to diagnose and replace, if necessary, an automatic transmission with Incorrect Ratio DTC (transmission clutch slip in gear above limit) listed on Page 2.
23-AT-003H-1	2023-09-06. Service bulletin. If you are servicing an 8-speed vehicle with a “Check Engine” light on and one or more of the DTC listed, follow the service procedure and replace the related solenoid and harness.
23-01-014H-5	2023-09-06. Service bulletin. Hyundai has launched an anti-theft software upgrade and window decal campaign (Campaign 993), combined with an anti-theft steering wheel lock campaign (Campaign P32), in response to an increase in thefts of certain 2011-2022MY Hyundai vehicles not equipped with engine immobilizers targeted through social media. For certain vehicles that cannot be updated with the software (Campaign 993), Hyundai is offering customers steering wheel locks at the dealer (Campaign P32). This Dealer Best Practices Guide provides information to assist dealership personnel with customer questions relating to the immobilizer software upgrade, window decals and steering wheel lock ant-theft solutions available from HMA through Hyundai dealers.
22-AT-007H	2022-06-10. Service bulletin. Certain vehicles (listed below) equipped with 7-speed Double Clutch Transmissions (DCT) may exhibit abnormal vibration at low speeds. This bulletin outlines the procedures for diagnosing clutch judder, updating the Transmission Control Unit (TCU) with revised logic, and/or replacing the Double Clutch.
22-AT-006H	2022-06-10. Service bulletin. If you are servicing an applicable vehicle with a “Check Engine” light on and one or more of the DTC listed below, follow the repair procedure and replace the related input/output speed sensor and harness.
22-AT-005H	2022-05-10. Service bulletin. If you are servicing an applicable vehicle with a “Check Engine” light on and one or more of the DTC listed below, follow the repair procedure and replace the related solenoid and valve body harness.
21-AT-014H	2021-09-17. Service bulletin. Certain vehicles (listed below) equipped with 7-speed Double Clutch Transmissions (DCT) may exhibit abnormal vibration at low speeds. This bulletin outlines the procedures for diagnosing clutch judder, updating the Transmission Control Unit (TCU) with revised logic, and/or replacing the Double Clutch.
20-AT-005H-1	2020-11-06. Service bulletin. If you are servicing an applicable vehicle with a “Check Engine” light on and one or more of the DTC listed below, follow the repair procedure and replace the related solenoid and valve body harness.
20-AT-020H	2020-10-08. Service bulletin. This bulletin provides a procedure to transfer pressure data to the TCU using GDS Mobile. This procedure is necessary to reduce the transmission learning time and improve the shift quality.
20-AT-019H	2020-06-06. Service bulletin. If you are servicing any of the vehicles listed below with a harsh and/or delayed shift, use the GDS as shown in the Service Procedure to measure shift engagement time.