Somewhere on the window sticker, in small print, sits a code like B5 or T3B70. It is the emissions certification, it is legally significant, and essentially nobody reads it.
We pulled it from 25,911 EPA records. Here is what is actually out there.
| Code | What it stands for | Records |
|---|---|---|
| B5 | Tier 2, Bin 5 | 10,186 |
| U2 | ULEV II (California) | 5,776 |
| L2 | LEV II (California) | 3,641 |
| B4 | Tier 2, Bin 4 | 3,280 |
| L3ULEV70 | LEV III ULEV70 | 3,148 |
| T3B70 | Federal Tier 3, Bin 70 | 3,121 |
| T3B125 | Federal Tier 3, Bin 125 | 2,895 |
| T3B30 | Federal Tier 3, Bin 30 | 2,622 |
Two systems, and they count differently
The codes come from two eras, and the confusing part is that both use bins while numbering them on opposite logic.
Tier 2 ran from 2004 and used bins 1 through 8, where lower is cleaner. Bin 5 was where most ordinary petrol cars landed, which is why it dominates the table with 10,186 records.
Tier 3 replaced it from around 2017 and renamed the bins after the actual pollutant target: the combined non-methane organic gases and nitrogen oxides in milligrams per mile. So T3B125 allows 125 mg/mile, T3B70 allows 70, and T3B30 allows 30.
That change is genuinely an improvement in clarity. Under Tier 2 you had to know that Bin 5 was cleaner than Bin 8; under Tier 3 the number is the limit.
The market moved down the scale
Sort our records by model year and the dominant standard shifts in a straight line.
From 2005 through 2019, BIN 5 is the most common certification in every five-year window. From 2020 to 2024 it is T3B70. For 2025 onward it is T3B30 — a limit less than a quarter of what T3B125 permitted a few years earlier.
The mechanism is a fleet average rather than a per-car rule. A manufacturer can sell some vehicles at a higher bin as long as the average across everything it sells meets the target, which is why several bins coexist in the same model year and why the mix drifts cleaner over time.
The California codes are a separate track
U2, L2 and L3ULEV70 are California standards — ULEV II, LEV II and LEV III — and their presence in the data reflects that a large group of states follows California rules rather than federal ones.
For a buyer this occasionally matters. A vehicle certified only to a federal standard can face registration friction when moved into a state that follows California, particularly on cars under a certain age. The sticker code is what determines it, which is one of the few practical reasons to care what the letters say.
Where to find it on a used car
Two places. The window sticker if it still exists — which for anything built before 2015 it almost certainly does not, since manufacturers only began keeping retrievable copies in the mid-2010s.
The reliable location is the emissions label under the bonnet, usually on the underside of the bonnet itself or on the strut tower. It is a printed sticker, it does not fade quickly, and it carries the certification level along with the vacuum routing diagram.
Anything else about the vehicle's identity — engine, plant, build specification — is encoded in the seventeen characters instead, and a free VIN check reads those.
Frequently asked questions
What does BIN 5 mean on a car?
It is the Tier 2 emissions certification level, and it was the most common standard in the US for fifteen years — 10,186 of the records we hold carry it. Tier 2 ran bins from 1 to 8 where lower is cleaner, and Bin 5 was the level most ordinary petrol cars were built to.
What is Tier 3 and how is it different?
The standard that replaced Tier 2 from around 2017. Its bins are named after the fleet average NMOG+NOx target in milligrams per mile, so T3B70 means Bin 70 and T3B30 means Bin 30. Lower is cleaner, and the number is directly comparable between bins in a way Tier 2's were not.
Which standard is on most used cars?
It depends on the model year. Cars from roughly 2005 to 2019 are mostly BIN 5. From 2020 the most common is T3B70, and 2025-onward records are dominated by T3B30 — the fleet is being certified progressively cleaner as manufacturers work toward the required average.
Does the emissions code affect me as an owner?
Mostly at inspection time and in states that follow California rules. A vehicle certified to a California standard (the LEV and ULEV codes) can be registered anywhere, but a federal-only vehicle can face restrictions when moving into a CARB state. The code on the sticker is what settles it.
Denis Kataev is a serial solopreneur and the founder of ForCar. With 15+ years in software engineering and 10 years in SEO, he builds data-driven products end to end — backed by a sharp eye for design. At ForCar he mines proprietary vehicle datasets, turning raw numbers into buying advice you can actually trust.
Keep reading
All articles →
510 People Asked for a Pre-2010 Window Sticker. None Exists.
The original window sticker is the single best document about how a car was sold. Whether it still exists depends almost entirely on one thing, and it is not the make, the model or the condition.
One Recall Covered 71 Different Models at Once
A recall usually means one manufacturer found one problem in one vehicle. Occasionally it means something else entirely, and those are the campaigns that reach across brands that compete with each other.
100,000 Miles Takes 7 Years in Louisiana and 12 in Hawaii
Odometer readings get judged against a single national rule of thumb, usually 12,000 miles a year. Split the same data by state and that rule turns out to be wrong in both directions, by enough to change what a number means.
Mark ForCar as a preferred source and our data shows up first in your Google results. One click, no account.