Porsche bulletin 2121.4
What it saysACC Dynamic Calibration Fault C110300 NHTSA’s full summary ↓
Porsche filed this with NHTSA as a service bulletin dated Jul 29, 2026, received Aug 5, 2026, about the vehicle speed control. It names 7 model years (2019–2025). 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.
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What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationACC Dynamic Calibration Fault C110300
Document filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| 2121.4 | Service bulletin | Jul 29, 2026 | 11035741 | PDF, 208 KB |
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.
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Model years it names
Source: as the manufacturer filed themA vehicle page’s bulletin list shows the newest few communications filed against that model year; the count there is every one.
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What owners reported
Source: NHTSA complaint databaseOwners of the 7 model years this bulletin names have filed 114 complaints with NHTSA since 2015. 14 of them name Forward Collision Avoidance, Vehicle Speed Control — 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.
At approximately 57 miles after delivery of a new 2025 Porsche Cayenne, the Adaptive Cruise Control (ACC) and related driver-assistance safety systems failed while the vehicle was traveling at approximately 67 mph. There had been no collision, impact, or abnormal event prior to the failure.
2025 Porsche Cayenne · Forward Collision Avoidance · filed with NHTSA Mar 5, 2026 · ODI 11722337
i was driving my car and at a stop sign i started accelerating when the light turned green - i must have been going 45 mPH after the light and all of a sudden my car went into hyper acceleration speeding up to 80 mph, i was pumping my brakes and the car was still raging to accelerate.
2023 Porsche Cayenne · Vehicle Speed Control · filed with NHTSA Sep 12, 2025 · ODI 11687005
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.
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Porsche, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is Porsche 2121.4 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 2121.4 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 Porsche warranty extension on file lists the ones Porsche has filed.
Which vehicles does 2121.4 cover?
The manufacturer filed it against 7 model years: 2025 Porsche Cayenne, 2024 Porsche Cayenne, 2023 Porsche Cayenne, 2022 Porsche Cayenne, 2021 Porsche Cayenne, 2020 Porsche Cayenne and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.