What does an EPA engine family name mean?

Almost every engine sold in the United States carries an emissions label, and on it a twelve-character engine family name. The first character is a model year code — which makes this, for a great many machines, the only date on them that anybody outside the factory can read.

Mowers, chainsaws, generators, pressure washers, outboards, snowmobiles, ATVs, motorcycles. Their makers mostly do not publish serial number schemes, and several of the compilations that do are not ours to reproduce. The emissions label is public, and this reads it from EPA’s own naming convention.

The code in the box is made up. It is assembled out of EPA’s own tables to show the shape — R for 2024, S for small nonroad spark-ignition — with XXX and ABC standing in for the two fields nothing on this page can decode. Type your own over it.

What it is made of

“A family name is a 12 character code that identifies all parts of that particular engine.”

EPA describe the layout like this:

“The first character is model year code, 2-4 are manufacturer code, 5 is industry sector code, 6-9 is engine displace code or family type descriptor code, and 10-12 is manufacturer's self-designated code.”

That sentence is alt text. It is the description attached to a diagram on EPA’s page, not a line of their prose and not a line of any regulation. It is EPA describing EPA’s own image, so it is theirs to state — but it is a thinner thread than a sentence in a statute, and this page would rather say so than quietly present it as settled.

EPA add their own warning in the prose, and it travels with everything below: “The typical naming convention is shown below, although some sectors have a slight variation.”

The model year code

Position 1. Thirty-nine codes, covering 2001 to 2039:

Five letters are never used

Look down the alphabet and I, O, Q, U and Z are not there. EPA do not say why, and this page is not going to invent a reason for them.

What can be said is that the first three are the three a VIN excludes as well, where the reason is on the record: they are too easily confused with 1 and 0. EPA drop two more on top of that.

And the code wraps after thirty years

1 to 9 is 2001 to 2009. Then the letters run to Y for 2030, and then 1 to 9 starts again for 2031 to 2039. Nine codes carry two years each, exactly thirty apart.

So a family name beginning 4 is 2004 or 2034, and nothing inside the name settles it. The tool above gives both readings rather than picking one. In practice the later half has not happened yet, and this paragraph has a shelf life.

Positions 2 to 4: the manufacturer

“This code is the 3-character, alpha-numeric code that EPA assigns to each company”

This page cannot turn those three characters into a company name. EPA assign the codes and hold the list in their Verify registration system. Guessing a maker from three characters against a list we do not have would be inventing an answer, so the tool says it is not decodable here and leaves it at that.

Position 5: the industry sector

Twenty-three codes, and note that three of them are digits — position 5 is not always a letter:

* EPA’s footnote, in full: “This also includes heavy-duty highway vehicles at or below 14,000 pounds GVWR that are not tested on a chassis-dynamometer for certification under 40 CFR Part 1037 (i.e., certified to the requirements and standards of §1037.105, per §1037.104(f)).”

One row of that table has no code

EPA list a twenty-fourth sector, Light-Duty Durability Group, and in the code column they put a sentence: “Various options based on Combustion Cycle”. It is not a character, and it is not a character this page can work out either.

So the table above has twenty-three rows where EPA’s has twenty-four. The missing one is missing because there is nothing to put in it, and saying that is better than making the table look tidier than the source.

Positions 6 to 9, and a decimal point that does real work

These four are usually the displacement. How you read them turns on a single character:

“In all cases, the displacement will be read in liters if a decimal point is included and it will be read in cubic inches or cubic centimeters if there is no decimal point.”

Read that twice, because of what it admits. A decimal point means litres. No decimal point, and EPA name two units without choosing between them — cubic inches or cubic centimetres. If the source does not settle it, this page does not settle it either.

The decimal point counts as one of the four characters, which is why a 1.6-litre engine has room for 1.60 and not much else. And for engines built in several sizes: “For dual or variable displacement families, enter the maximum displacement.”

These four are not always a displacement at all. EPA call them “engine displace code or family type descriptor code” — and then send you somewhere else entirely:

“Click on your industry sector to view specific instructions for determining Positions 5-12 of your family name.”

So everything from position 5 onwards is defined per sector, on twenty-odd separate pages. What is above is the general shape EPA describe, with their own warning that some sectors vary attached to it. This page does not claim to have read all twenty-odd.

Positions 10 to 12: the maker’s own

“Manufacturer’s self-designated code”. Three characters that mean whatever the manufacturer decided they mean. There is nothing to decode, by anybody, and no lookup table exists that would help.

This is guidance, not regulation

Worth being plain about, because most of the other pages on this site are reading a statute. The twelve characters are not in the Code of Federal Regulations.

40 CFR 1060.135 requires the family on the label “using EPA’s standardized designation” — and stops there. Parts 1054, 1045, 1051, 1048, 1039, 86 and 90 were read too, and none of them gives the character layout. The one promising hit, “12 characters” in part 1060, turns out to be about how big the label has to be.

That makes this the fifth source on the site to define a structure and hand part of it to somebody else, after the railway act, the Hallmarking Act, 47 CFR 2.926 and the egg directive. Four of those delegate to an agency. This one delegates to the agency that wrote it.

Where to find it on the machine

On the emissions label, which is generally a sticker or a stamped plate on the engine itself rather than on the machine around it. The heading varies: Engine Family, Family, Engine Family Number or Test Group are all the same field. EPA use several words for the thing a family name names — engine family, test group, vehicle family, durability group, evaporative family — and the twelve characters work the same way in each.

It is not the serial number and it is not the model number. If the code you have is not exactly twelve characters, it is one of those.

A note on where this came from

EPA publish the naming convention on their Vehicle and Engine Certification site, and their Standard Open Data License states that “all data produced by the U.S EPA is by default in the public domain and is not subject to domestic copyright protection under 17 U.S.C. § 105”. Their robots.txt permits the fetch. Their document archive at nepis.epa.gov does not, and was not touched.