BMW bulletin B520121
What it saysSEAT FAILS TO INITIALIZE DUE TO MISSING END STOP: Front seat will not calibrate/initialize. NHTSA’s full summary ↓
BMW filed this with NHTSA as a service bulletin dated Aug 1, 2023, received Mar 15, 2021, about the seats — 3 documents under this number. It names 60 model years (2016–2023). 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.
Get the next BMW bulletin for your model by email Weekly, only when something new is filed. Nothing else; one-click unsubscribe.
What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationSEAT FAILS TO INITIALIZE DUE TO MISSING END STOP: Front seat will not calibrate/initialize.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| B520121 | Service bulletin | Aug 1, 2023 | 10242694 | not found |
| B520121 | Service bulletin | Jun 1, 2021 | 10200234 | not found |
| B520121 | Service bulletin | Feb 1, 2021 | 10188945 | not found |
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 themand 6 more on this site: 2023 BMW X7, 2022 BMW X7, 2021 BMW X7, 2020 BMW X7, 2019 BMW X7, 2023 BMW i7.
Also filed against model years this site has no page for: 2019 BMW 540D; 2020 BMW 540D; 2020 BMW 640I; 2018 BMW B7 Alpina; 2019 BMW B7 Alpina; 2020 BMW B7 Alpina; 2021 BMW B7 Alpina; 2018 BMW C 400 X; 2021 BMW F 850 GS Adventure; 2017 BMW F800 R; 2021 BMW M760LI; 2022 BMW M760LI; 2018 BMW R Nine T Scrambler; 2017 BMW R1200 RT Police.
A vehicle page’s bulletin list shows the newest few communications filed against that model year; the count there is every one.
Email me new BMW bulletins for one of these models
A weekly email, sent only in a week when BMW files something new with NHTSA for the model you pick — service bulletins, campaigns, warranty extensions, over-the-air notices, every model year. Nothing else is sent; one-click unsubscribe in every message. Separate from recall alerts.
What owners reported
Source: NHTSA complaint databaseOwners of the 46 model years this bulletin names have filed 1,668 complaints with NHTSA since 2015. 40 of them name Seats — the same broad component group this bulletin is filed under. NHTSA groups complaints coarsely, so that means the same area of the vehicle, not necessarily the same fault.
Constantly pops up a message for passenger restraint system malfunction. I had an accident where I swerved off the road into a ditch at about 60 mph. I the driver was not hurt and the passenger wouldn’t have been hurt either if it was for the passenger seat belt not locking correctly at first and then repeatedly locking and unlocking the…
2018 BMW 5 Series · Seats · filed with NHTSA Feb 9, 2025 · ODI 11641549
Front driver seat , keep sliding when u hit on breaks on the left legs where seat controls are located the balance between right thigh and left thigh is not well measured so becomes increasingly uncomfortable when thicker person driving the car, could cause an accident and risky, Engine problem - so many coolant leak which has cost me…
2018 BMW 4 Series · Seats · filed with NHTSA Nov 24, 2024 · ODI 11627063
The Passenger Restraint System was failing and is now constantly showing a Passenger Restraint System alert. It can not tell whether a passenger is in the seat or not. A local BMW specialist says it is a common issue with the passenger occupancy mat
2017 BMW 4 Series · Seats · filed with NHTSA May 10, 2024 · ODI 11588043
A complaint is one owner’s account, not a defect finding, and a bulletin is not a recall. Nothing here says this bulletin was issued because of these complaints, or that the repair it describes fixed them. Complaint files on this site begin in 2015.
More bulletins about the seats
Source: same model, same component group16 other manufacturer communications filed against these BMW models under the same component group (seats), newest first. The eight newest are listed; the rest are on the BMW list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| 0061780900 | Service campaign | Sep 10, 2026 | The seat module for the driver’s seat maycontain an incomplete solder connection. Ifthis connection breaks over time, the seat canonly be ad… |
| B611726 | Service campaign | Aug 27, 2026 | Delivery Stop - Front Seat Module |
| B520120 | Service bulletin | Jun 27, 2026 | GROANING NOISE FROM TRIM APERTURE ON THE FRONT SEAT: When getting in or out of the vehicle a groaning noise can be heard from the opening… |
| B521923 | Service bulletin | May 4, 2026 | In vehicles equipped with the second row 60% / 40% split seat, the flex cable assembly can come out of the seat rail mechanism (circled).… |
| B520126 | Service bulletin | Mar 9, 2026 | The customer brings vehicle in with one or both of the second row 60/40 split seats in the folded position. The seat does not respond to any… |
| B520920 | Service bulletin | Aug 19, 2025 | Various concerns about the third row of seats (3SR): 1. Head restraint (aka headrest), on one or both sides, cannot be folded down. 2. Third… |
| B520825 | Service bulletin | Jun 17, 2025 | The rear seat leg rest can fold down when a heavy load/weight is placed on it. |
| B520524 | Service bulletin | Aug 7, 2024 | A rattling noise can be heard emanating from the area of the rear seat backrest of the second row ofseats. The noise does not occur when the… |
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for BMW, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is BMW B520121 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 B520121 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. Every BMW warranty extension on file lists the ones BMW has filed.
Which vehicles does B520121 cover?
The manufacturer filed it against 60 model years: 2022 BMW 2 Series, 2021 BMW 2 Series, 2020 BMW 2 Series, 2020 BMW 4 Series, 2019 BMW 4 Series, 2018 BMW 4 Series and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.