Why VINs Never Use the Letters I, O or Q (and What to Do If Yours Does)

A modern 17-character VIN never contains the letters I, O or Q. The federal VIN rule, 49 CFR 565.13, lists the only letters a VIN may use, and those three are left out, mainly so nobody mistakes them for the numbers 1 and 0. So if the VIN you copied down has an O in it, it's almost always a zero, an I is a one, and a Q means you misread something. Fix it before you pay for a report, or you'll be paying to look up a car that doesn't exist.

I checked the regulation text on eCFR and then ran a few deliberately broken VINs through NHTSA's free vPIC decoder on Saturday evening, October 17, 2026. The rule was what I expected. What the decoder did with the bad characters was more interesting, and it's a good reason not to trust a decoder result at a glance.

What the federal rule allows

Section 565.13(g) says each character must be one of the letters ABCDEFGHJKLMNPRSTUVWXYZ or a numeral from 0 to 9. Count them and you get 23 letters, with I, O and Q missing. The same section says every one of the 17 positions has to be filled with one of those characters and that VINs use capital, sans-serif type. The definitions section calls a VIN a series of Arabic numbers and Roman letters, so lowercase letters and symbols are out too.

The regulation never says why those three letters are banned. Car and Driver's VIN guide says I, O and Q are excluded because they could be confused with 1, 0 and 9, and The Drive gives the same reason with 1 and 0 only. They differ on whether Q is a 0 or a 9 risk, but the logic is the same: on a dirty dash plate or a faded title, round letters and zeros look alike, so the system just doesn't use the letters.

Spots in the VIN with even tighter rules

Some positions allow fewer characters than the rest. Position 9 is the check digit, and Part 565 says it must be 0 through 9 or the letter X. Our check digit explainer walks through the math, which is handy here, because swapping an O for a 0 will usually break the check digit.

Position 10 is the model year, and the code table in Part 565 skips U, Z and the number 0 on top of I, O and Q. That's why 2026 models carry a T and 2027 models jump straight to V, so you'll see V on new 2027 cars on lots this fall, never U. Our 10th digit model year guide has the full table. And on passenger cars and light trucks, the rule requires the last five characters to be numeric, so anything that looks like a letter in positions 13 through 17 is a misread, as our serial number post explains.

What vPIC does with an O, I or Q

I started with a VIN that decodes cleanly, a 2013 Ford F-150 with the 3.5-liter V6 built in Dearborn, then swapped in bad letters through the vPIC API. With an O replacing the zero in position 14, vPIC returned error 400, "Invalid Characters Present," named the spot as "14:O," flagged the check digit as wrong and offered a suggested VIN with an exclamation mark where the O had been. It still showed Ford, F-150 and 2013, though, because the first ten characters were intact. A Q in position 13 did the same thing.

Putting an I in position 1 was different. vPIC added an error saying the manufacturer isn't registered with NHTSA and returned no make or model at all. So the takeaway is uncomfortable: a bad character in the back half of the VIN can still produce a decode that looks fine if you only read the make and year. Always read the error line on the vPIC decoder, not just the vehicle details.

When you actually see an I, O or Q

Usually it's a copying mistake, so go back to the car. Compare the dash plate, the door-jamb label and the title, using our guide on where to find the VIN on a car. If the title itself shows an O, ask the seller to get it corrected at the DMV before you buy, because a title that doesn't match the car is a problem you'd inherit; see our post on a VIN on the title that doesn't match the car.

If the stamped plate on a 1981 or newer car really shows one of those letters, stop. A legitimate factory plate shouldn't have one, so you could be looking at a homemade or swapped plate, and our VIN cloning guide covers what to check next. Pre-1981 cars are a separate case, since they came before the 17-character format; our post on a VIN shorter than 17 digits covers those.

Before you run a report

Get the corrected VIN to pass vPIC with no error 400 and a valid check digit, then search it in NMVTIS for title brands. If a history site comes back empty, read our post on no records found before assuming the car is clean. CarVins is a licensed CARFAX and AutoCheck reseller, not affiliated with CARFAX, AutoCheck or Experian. In mid October 2026, a report costs about $5.50 as a guest, roughly $4.50 for members, or around $6.75 for both, against retail of $39.99 to $44.99. Prices move, so the checkout page has the final word.

Sources

• 49 CFR 565.13 (eCFR), including the Part 565 year-code table
• NHTSA vPIC decoder and vPIC API, tested Oct. 17, 2026
• Car and Driver: How to Decode a VIN; The Drive on VIN letter rules
• NMVTIS