The RPO -- regular production option -- codes for most cars are pretty easy to come by; there are massive lists of them available online. However, that doesn't help many older GM car owners, because it was up to the particular assembly plant to decide how it was going to list the car's options. Some were very helpful, and put the RPO codes right on the VIN tag; others used a frustrating and cryptic system known as the "ACC" or "accessory" code to save space. Information on these ACC codes is generally scarce, which makes knowing what you're looking at that much more difficult.
The ACC Coding System
Once you know how the ACC coding system works, it's fairly easy to read the codes. An example would be "EF2EM3C4M5V." Chevrolet assembly plants broke the options down into five groups, with "Group 1" being denoted by by the "E" in the ACC code. The letters that followed each number corresponded to the car's options within that group, so you need to start by breaking the code down into the number and letter groups. The above code would break down as: EF- 2EM - 3BC - 4M - 5V. So, this car has option Code "F" in Group 1, Codes "E" and "M" in Group 2, "B" and "C" in Group 3, and so on. This code breaks down as a car with tinted glass, air conditioning, a Powerglide transmission, rear window defogger, padded dash, a 375-horse 396 engine and seat belts.
There were four codes used in Group 1 in the 1964 model year. Code "E" is RPO A01 tinted glass, Code "F" is an A42 power bench seat, Code "G" is an A33 power tail gate for station wagons, and Code "W" is an A02 tinted windshield. Option codes not available in 1964 included a Code "D" C06 power top, Code"L" fold-down rear seat, Code "T" power bucket seats, Code "X" A31 power windows and Code "O" for two-tone paint. Codes "B" and "Y" were also used in other years, but they indicate the model year. Code "Y" is a 1965 or 1966 car, and Code "B" indicates it's a 1967 car.
For 1964, there were about a half-dozen codes in use. Code "L" is an M20 four-speed manual, which could mean a Muncie M21 or M22 transmission. Code "M" is an M35 Powerglide Code "P" is an option package that includes a U63 push-button radio, and the Z13 back-up lights and remote mirror. Code "A" says Turbo 400 transmission, Code "R" indicates a U80 rear-seat speaker, and Code "S" indicates a rear manual antenna. Codes for other years include a Code "B" three-speed floor-shifter, Code "K" or "E" air conditioning, Code "G" console and Code "H" is a heater delete. Code "U" is a stereo tape system. Code "Z" translates to a convertible rear speaker, Turbo 400 transmission and a tilt steering wheel.
In 1964, you'd find Code "B" for a C50 rear window defogger, Code "C" for a B70 padded dash, Code "D" for the Z01 "special lighting group or Code "J" for J65 metallic brake pads. Cars from model year 1967 were available with the Code "K" exterior chrome trim package, Code "L" Rally sport and power steering package, or Code "S" interior chrome.
For model years other than 1964, this group would largely include engine options. However, in 1964 alone, Group 4 included only the Code "F" Z01 comfort and convenience package. In 1965, it came to include Code "M" for the Z16 375-horse 396 engine, Code "P" for a right-side rear-view mirror, and Code "U," which was used only on Chevrolet Corvairs. In 1967, Group 4 expanded further to include a Code "D" rear window defogger, Code "F" remote mirror, Code "K" L78 396 engine, Code "L" Z28 302 engine, Code "N" L35 325-horse 396 engine and Code "P" for the L48 350 engine. Not all of these were available on the Impala, most notably the Z28 302 engine.
Group 5 is especially helpful when spotting cars, because it contains a few codes that are model-year specific. There were four options available in Group 5 in the 1964 model year. These included Code "O" exterior chrome, Code "V" A37 seat belts, Code "W" passenger side mirror and Code "Y" A49 "deluxe" padded seat belts. Code "Z" debuted in 1966, indicating three-point, shoulder-harness seat belts, and Code "V" hit Chevrolets in 1967, indicating stylish V30 bumper guards. If you're car-spotting, Code "L" denoted a 1965 car, and both "C" and "M" were reserved for 1967 Chevys.