23PBJ – Delayed Trailer Brake Release – 2020-2024 Peterbilt 548, 536, & 2024 537

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September 29, 2023 NHTSA CAMPAIGN NUMBER: 23V661000

Delayed Trailer Brake Release/FMVSS 121

A delay in the trailer brake release can create instability to the trailer and increase the risk of a crash.


NHTSA Campaign Number: 23V661

Manufacturer PACCAR Incorporated


Potential Number of Units Affected 257



PACCAR Incorporated (PACCAR) is recalling certain 2021-2024 Kenworth T280, T380, 2020-2024 Peterbilt 548, 536, 2024 Peterbilt 537, and 2020-2024 Kenworth T480 trucks. The timing of the trailer brake release may be delayed. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 121, “Air Brake Systems.”



Dealers will replace the fittings and hoses in the affected valves, free of charge. Owner notification letters are expected to be mailed November 20, 2023. Owners may contact Kenworth’s customer service at 1-425-828-5888 and Peterbilt’s customer service at 1-940-591-4220. PACCAR’s numbers for this recall are 23KWJ and 23PBJ.



Owners may also contact the National Highway Traffic Safety Administration Vehicle Safety Hotline at 1-888-327-4236 (TTY 1-800-424-9153), or go to www.nhtsa.gov.


Certain 536, 537, and 548 chassis built with 2.1m Medium Duty End of Frame Trailer Connections may exceed the standard trailer brake release timing requirements by 0.5 seconds due to the size of the tractor protection valve fitting and hose. A delay in the trailer brake release can create instability to the trailer and increase the risk of a crash.

Parts and repair procedures are not yet available. This bulletin will be updated when a repair path is determined.


Certain 536, 537, and 548 chassis built with 2.1m Medium Duty End of Frame Trailer Connections may exceed trailer brake release timing requirements of FMVSS/CMVSS No. 121 by 0.5 seconds. A delay in the trailer brake release can create instability to the trailer and increase the risk of a crash. Truck and Trailer brake application timing is not affected, nor is brake performance affected.


Chronology :

07/07/23 – Engineering notified Safety & Compliance that brake timing test failed for a new model that used the same 2.1m Medium Duty end of frame tractor protection valve.

07/12/23 – Engineering began researching 2.1m Medium Duty configurations that have been built.

07/14/23 – PACCAR Technical Center continued brake timing tests for 2.1m Medium Duty to determine which configurations would not pass.

08/23/23 – Brake timing tests completed. Engineering created compatibility message to flag trucks in the backlog to get corrected.

09/08/23 – Engineering provided list of trucks in backlog already corrected.

09/11/23 – Plant provided list of trucks still at plant for Safety & Compliance to review which need to be corrected.

09/14/23 – Joint Safety Committee determined a regulatory non-compliance exists.

As of 09/14/23, Paccar received 0 warranty claims and 0 reports about 0 trucks in the field that may be related. 0 reports of deaths or injuries have been received.


24 Affected Products


KENWORTH T280 2021-2024
KENWORTH T380 2021-2024
KENWORTH T480 2020-2024
PETERBILT 536 2020-2024
PETERBILT 537 2024
PETERBILT 548 2020-2024


3 Associated Documents

Noncompliance Notice 573 Report

RCLRPT-23V661-4548.PDF 216.565KB

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Recall Acknowledgement

RCAK-23V661-9386.pdf 646.034KB

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Safety Bulletin

RCSB-23V661-7015.pdf 106.985KB

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Last update on 2024-06-10 / Affiliate links / Images from Amazon Product Advertising API

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