Chevy & GMC Truck RPO Code Decoder

Type in the codes from your truck’s Service Parts Identification sticker, the RPO code label in the glove box, and the decoder tells you what each one means: the engine, transmission, axle ratio, trim level and every factory option the truck was built with. It reads 1973-⁠87 square body, 1988-⁠98 OBS and S10 / S15 trucks, Chevrolet and GMC, then takes you straight to the parts that fit.

Where to find the RPO code sticker

GM calls it the Service Parts Identification label. It is a paper sticker printed with the VIN, the model number and a grid of three-character option codes. Where to look:

• 1973-⁠74: often under the hood, on the driver’s side inner fender below the brake master cylinder.
• Mid-1970s to 1987: on the inside of the glove box door. A few trucks still have it on the inner fender.
• 1988-⁠98: on the inside of the glove box door, headed “Service Parts Identification”.
• S10 and S15: usually on the back of the glove box door.

A faded label is easier to read in a photo. Take one with the flash on at a slight angle, then zoom in. Trucks from 1967-⁠72 used an earlier layout with numbers in front of each code, so this decoder starts at 1973.

How to read an RPO code label

The top of the label carries the VIN and the model number (CK10903, for example). Under that is the grid of three-character codes. Each code is one option or piece of equipment, and they are not in any particular order. The paint codes sit on their own line at the bottom.

Copy every code into the decoder, in any order. You don’t need to tell it which ones are the engine or the axle, and you can paste the VIN in with them. If you are not sure which era your truck is, leave it on “Not sure” and the decoder works it out from the codes, or from the VIN if you include it. Then use the Chevy truck VIN decoder to confirm the year, series and plant.

What RPO codes can and can’t tell you

The label records how the truck left the plant. It can’t tell you what has been changed since. Engine and gearbox swaps, rear end swaps and replaced glove box doors are common on these trucks, so check what is actually on the truck as well as what the sticker says. The parts interchange checker shows which years’ parts bolt on.

A few things trip people up:

• Sales codes. MX0, MX1, MM3, MM4 and MM5 only say automatic or manual. The code for the actual gearbox, such as M40 or MD8, sits elsewhere on the same label.
• Reused codes. GM gave some codes new meanings over the years. UM2 was an 8-track in the 70s and a CD-ready cassette in the 90s, so the era you pick matters.
• Codes we don’t list. GM issued thousands of RPO codes. Many are interior colors, plant and shipping codes. Our list covers the ones that tell you something useful about the driveline, the trim and the options.

The square body guide and What is an OBS truck? cover what changed year to year on each generation.

GM RPO code list for 1973-⁠98 Chevy and GMC trucks

Every code the decoder reads, grouped by what it covers. Search for a code or a word, or narrow the list to your era.

Common questions

What does RPO stand for?

Regular Production Option. It is GM’s three-character code for each option a vehicle could be ordered with. The same codes were used on the order sheet, at the plant and at the parts counter, which is why they are printed on the truck.

What does G80 mean on a Chevy truck?

G80 is the locking rear differential, an Eaton automatic locker often called a Gov-Lok. It is not a clutch-type Positraction, even though GM’s own 1973 text calls it that. On GM cars the same code means limited slip.

What gear ratio does my truck have?

Look for the axle ratio code on the label: GU6 is 3.42, GT4 is 3.73, GT5 is 4.10 and HC4 is 4.56. Paste the label into the decoder and it picks the ratio out for you. If the rear end has been swapped, the tag on the axle is the better guide.

What is the difference between YE9 and Z62?

YE9 is the top trim: Silverado or Sierra Classic on a square body, Silverado or SLE on an OBS. Z62 is the step below: Scottsdale or High Sierra on a 1982-⁠87, Scottsdale or SLX on an OBS. Before 1975 the trim names were different, and the decoder shows those too.

Can I get my RPO codes from the VIN?

Not from the VIN itself. It carries the year, plant and series, and on later trucks the engine, but not the options. On these trucks the sticker is the only place on the truck where the full option list was printed. The VIN decoder reads everything the VIN does hold.