Reading Hidden Codes on Your Car [Tire Dates, VINs, Fuses]
Your car carries its specifications in small stamped and printed codes: the tire DOT code ends in a four-digit week-and-year manufacture date, the 17-character VIN encodes model year and plant, the door jamb sticker lists paint code and correct tire pressure, and the fuse box lid maps each fuse. Reading them correctly means ordering the right parts and knowing how old your tires really are.
Most of what you need to know about your car is written on it somewhere, in text small enough that nobody reads it until something goes wrong. Tire age, paint color, the right bulb, which fuse feeds the radio. Here is where those codes live and how to read them.
Tire DOT codes: how old are your tires
Every tire sold in the United States carries a code on the sidewall beginning with the letters DOT. The full code identifies the plant and tire size, but the part that matters to you is the last four digits, which give the week and year of manufacture. A code ending in 2324 was made in the 23rd week of 2024. One ending in 0819 was made in week 8 of 2019.
Rubber hardens and cracks with age even if the tread looks fine. Many manufacturers suggest an inspection once tires pass five or six years and replacement once they reach ten, regardless of tread. The date code is how you know where you stand, and it is also how you catch a "new" tire that has been sitting in a warehouse for years.
The date code is molded in low relief, often black on black, and is only required on one sidewall. If you cannot find it, check the inner side. A flashlight held at a low angle makes the raised characters cast small shadows; in LoupeLens, 3x zoom with the flashlight dimmed slightly is enough to read them without glare.
Other sidewall markings
- Size, such as 225/45R17, gives width in millimeters, aspect ratio, construction, and rim diameter in inches.
- Load index and speed rating follow the size, for example 94V.
- Max pressure on the sidewall is the tire's limit, not your recommended pressure. See the door jamb section below.
- Tread wear indicators are raised bars in the grooves. When the tread is flush with them, the tire is at the legal minimum in the US.
The VIN
The vehicle identification number is 17 characters long and appears at the base of the windshield on the driver's side, on the door jamb sticker, and on your registration and insurance documents. It never uses the letters I, O, or Q, to avoid confusion with 1 and 0.
The tenth character encodes the model year, and the eleventh the assembly plant. Parts suppliers and recall lookups key on the VIN, so getting every character right matters. Reading it through the windshield at an angle is a common source of errors; take a photo and read the still image rather than transcribing from the live view.
The door jamb sticker
Open the driver's door and look at the pillar or the door edge. One or more stickers here are the most useful text on the car.
- Tire pressure placard. The pressures listed here are what the manufacturer specified for this car. Inflate to these, not to the sidewall maximum.
- Paint code. Usually labeled as paint, color, or with a short alphanumeric code near the bottom. On some makes the code is under the hood or in the trunk instead. You need this code to buy touch-up paint that actually matches.
- Gross vehicle weight rating and axle ratings, which matter if you tow or haul.
- Month and year of manufacture, which is not the same as the model year.
These stickers fade and get scuffed. Photograph them now while they are legible and keep the photo with your other car documents.
Fuse boxes
Most cars have two fuse boxes, one in the engine bay and one in the cabin, often under the dash or behind a kick panel. The lid usually has a diagram that maps each position to a circuit, using abbreviations or icons that are printed small and molded in the same color as the plastic.
The fuses themselves carry their amperage on the top in tiny numerals, and are color coded: for standard blade fuses, 10 A is red, 15 A blue, 20 A yellow, 30 A green. A blown fuse shows a broken or melted strip inside the clear body, which is much easier to confirm at 5x than by squinting.
Always replace a fuse with the same rating. A fuse puller is usually clipped inside the box. If you work under the dash, use the rear camera in LoupeLens with the flashlight on, take a photo of the fuse box label, then sit upright and read the photo instead of squinting in the footwell.
Under the hood
Oil filler cap
The cap is often stamped with the recommended viscosity, such as 0W-20 or 5W-30. This is a quick sanity check when you are standing in the store aisle. The owner's manual remains the authority, since some engines accept more than one grade depending on climate.
Belts and hoses
Belts are printed with a part number along their back. Hoses carry inner diameter and a spec code. Both fade under heat, so photograph them before they become unreadable and you will have the number when a replacement is due.
Battery
The battery label shows the group size, cold cranking amps, and often a date code sticker. Many brands use a letter for the month and a digit for the year, though schemes vary by manufacturer.
Bulbs, wipers, and other small parts
Bulb type is molded into the base of the bulb and sometimes into the housing behind it, in characters a couple of millimeters tall. Wiper blades often have their length stamped on the frame. Reading these directly avoids the guesswork of the store lookup chart, which is frequently wrong for trim variants.
Quick reference
| Code | Where | What it tells you |
|---|---|---|
| DOT date (last 4 digits) | Tire sidewall | Week and year of manufacture |
| VIN | Windshield base, door jamb | Model year, plant, exact identity |
| Tire pressure placard | Door jamb | Correct inflation for this car |
| Paint code | Door jamb, hood, or trunk | Exact color for touch-up |
| Fuse diagram | Fuse box lid | Which fuse protects which circuit |
| Oil grade | Filler cap | Recommended viscosity |
Working in the dark and at awkward angles
Nearly all of these codes are in poorly lit places at angles that make reading them uncomfortable. Three things help regardless of what tool you use: bring your own light, hold it low so raised text casts shadows, and capture a photo so you can read it comfortably afterward. A phone does all three at once, and the photo doubles as a record you can pull up at the parts counter.
For the general technique, see how to use your phone as a magnifying glass, and for other hard-to-read labels around the house, reading serial and model numbers.
Frequently asked questions
How do I read the date code on a tire?
Find the sequence on the sidewall that starts with DOT. The last four digits are the week and year of manufacture, so 1522 means the 15th week of 2022. The full code may appear on only one side of the tire, so check the inner sidewall if you cannot find it.
Where is the paint code on my car?
Most commonly on the sticker in the driver's door jamb, labeled paint, color, or with a short code near the bottom. Some manufacturers place it under the hood, in the trunk, or in the glove box. Your dealer can also look it up from the VIN.
Should I inflate tires to the pressure on the sidewall?
No. The sidewall number is the maximum the tire can safely hold. The correct pressure for your car is on the placard in the driver's door jamb or in the owner's manual, and it is usually noticeably lower.
How can I tell if a car fuse is blown?
Pull the fuse and look through the clear body at the metal strip. An intact fuse has a continuous S-shaped or straight strip; a blown one has a visible gap or a melted, darkened section. At 5x magnification the break is obvious. Replace it with a fuse of the same amperage.