Kenworth bulletin E304
What it saysPACCAR MX-11 and MX-13 EMY2016 NOx and N2O Exceedance Emissions Recall Certain vehicles with PACCAR MX-11 and MX-13 EMY2016 engines with less than 300,000 miles (482,803 km) have been shown, in testing, to exceed… NHTSA’s full summary ↓
Kenworth filed this with NHTSA as an emissions communication dated Mar 21, 2026, received Nov 10, 2023, about the engine — 2 documents under this number. It names 15 model years (2016–2018). An emissions communication is not a safety recall — there is no NHTSA campaign number and no federal requirement — but it is usually work the manufacturer pays for on the vehicles it names; the dealer checks the VIN against the manufacturer’s list.
What the bulletin says
Source: NHTSA's summary of the manufacturer's communicationE304: PACCAR MX-11 and MX-13 EMY2016 NOx and N2O Exceedance Emissions Recall Certain vehicles with PACCAR MX-11 and MX-13 EMY2016 engines with less than 300,000 miles (482,803 km) have been shown, in testing, to exceed regulatory limits for NOx and N2O emissions. This bulletin now applies to both Canadian and U.S.-registered vehicles. Software is now available to remedy this emissions non-compliance. NOTE California-registered vehicles that received a letter must have the software updated AND California documentation completed regardless of vehicle mileage.
Documents filed under this number
| Document | Kind | Dated | NHTSA id | At NHTSA |
|---|---|---|---|---|
| E304 | Emissions | Mar 21, 2026 | 11030931 | PDF, 2,448 KB |
| E304 | Service bulletin | Oct 18, 2023 | 10244494 | PDF, 770 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.
Model years it names
Source: as the manufacturer filed themAlso filed against: 2016 Kenworth T660; 2017 Kenworth T660; 2018 Kenworth T660; 2016 Kenworth T680; 2017 Kenworth T680; 2018 Kenworth T680; 2016 Kenworth T800; 2017 Kenworth T800; 2018 Kenworth T800; 2016 Kenworth T880; 2017 Kenworth T880; 2018 Kenworth T880; 2016 Kenworth W900; 2017 Kenworth W900; 2018 Kenworth W900.
None of these model years has a page on this site (it covers EPA-certified cars, trucks and SUVs from 2016), so the bulletin is listed here on its own.
More bulletins about the engine
Source: same model, same component group14 other manufacturer communications filed against these Kenworth models under the same component group (engine), newest first. The eight newest are listed; the rest are on the Kenworth list.
| Number | Kind | Dated | NHTSA’s summary |
|---|---|---|---|
| E340 | Emissions | Oct 16, 2026 | KW Certain vehicle model year 2026 Kenworth chassis equipped with EMY2025 PACCAR MX engines require an amended engine label. The engine labe… |
| P001 | Service campaign | Sep 11, 2026 | "KW: The chassis list has been updated to include 1 chassis. The total chassis count is now 53. A link to the PACCAR Powertrain Prognostics… |
| P003 | Service campaign | Sep 3, 2026 | "KW: A link to the PACCAR Powertrain Prognostics Webcast has been added in the Links section. PB: The chassis list has been updated to incl… |
| P002 | Service campaign | Sep 3, 2026 | "KW: A link to the PACCAR Powertrain Prognostics Webcast has been added in the Links section. PB: The chassis list has been updated to incl… |
| E335 | Emissions | Jul 18, 2026 | Expiration Date Format Update - Certain EPA21 compliant PACCAR MX-13 engines were built with intake valve springs that could fail. This fail… |
| CE033 | Warranty extension | Jun 25, 2026 | "KW & PB 14 fuel injector part numbers (seven for MX-11 and seven for MX-13 engines) have been added to this warranty policy." |
| CE031 | Warranty extension | Jun 24, 2026 | "KW & PB 14 fuel injector part numbers (seven for MX-11 and seven for MX-13 engines) have been added to this warranty policy." |
| 99-051 | Emissions | May 18, 2026 | There is an update to the CARB Base Emissions Warranty Limits table and Manufacturer’s Warranty Coverage section in certain Engine Model Yea… |
Quote the number at the service desk. It is what the dealer’s system is keyed on.
Every manufacturer communication NHTSA holds for Kenworth, by the number printed on the letter.
Common questions
Source: NHTSA, 49 CFR 579.5Is Kenworth E304 a recall?
No. A emissions communication 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.
Is the E304 repair free?
A emissions communication is usually paid by the manufacturer on the vehicles it names, within the terms and time limit the document sets; the dealer checks the VIN against the manufacturer’s list.
Which vehicles does E304 cover?
The manufacturer filed it against 15 model years: 2016 Kenworth T660, 2017 Kenworth T660, 2018 Kenworth T660, 2016 Kenworth T680, 2017 Kenworth T680, 2018 Kenworth T680 and more. Whether one particular vehicle is affected is a matter of its VIN and its build, not its model year alone.