BMW bulletin B340921
BMW filed this with NHTSA as a service bulletin dated Jan 14, 2025, received Nov 8, 2021, about the service brakes — 3 documents under this number. It names 18 model years (2016–2022). A service bulletin is not a safety recall: it is the manufacturer telling its dealers how to diagnose or repair a condition, and whether the work is paid for depends on the warranty in force. Quoting the number at a service desk can save a diagnosis.
What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationA turbine-like noise can be heard from the rear axle while deceleration during the first 300 miles of operation when braking from low speed.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| B340921 | Service bulletin | Jan 14, 2025 | 11013041 | not yet checked |
| B340921 | Service bulletin | Feb 1, 2023 | 10233158 | not yet checked |
| B340921 | Service bulletin | Sep 1, 2021 | 10203335 | not yet checked |
The summary is NHTSA’s abstract of the document, as filed under 49 CFR 579.5. One communication is usually filed as several documents — the bulletin, a dealer notice, an owner letter — and the number on any of them finds this page. A PDF link is shown only once NHTSA’s own server has been seen to serve that document; the rest are checked over the following nights. Quote the number at a service desk; it is what the dealer’s system is keyed on.
Model years it names
Source: as the manufacturer filed themAlso filed against model years this site has no page for: 2019 BMW M2; 2020 BMW M2; 2021 BMW M2; 2022 BMW M2; 2022 BMW M3; 2016 BMW M4; 2017 BMW M4; 2018 BMW M4; 2019 BMW M4; 2020 BMW M4; 2021 BMW M4; 2022 BMW M4.
A vehicle page’s bulletin list shows the newest few communications filed against that model year; the count there is every one.
Common questions
Source: NHTSA, 49 CFR 579.5Is BMW B340921 a recall?
No. A service bulletin is a manufacturer communication filed with NHTSA under 49 CFR 579.5; a safety recall carries an NHTSA campaign number (two digits, a letter, six digits) and a federal duty to repair for free. Check the vehicle’s recalls by VIN at nhtsa.gov/recalls, or on its page here.
Is the B340921 repair free?
Not automatically. A service bulletin describes how to diagnose or repair a condition; who pays depends on the warranty in force, any extension, and the dealer. Quoting the number can save a diagnosis either way.
Which vehicles does B340921 cover?
The manufacturer filed it against 18 model years: 2021 BMW M, 2020 BMW M, 2019 BMW M, 2018 BMW M, 2017 BMW M, 2016 BMW M and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.