Oh, the Wild West days of OBD-I, when freedom reigned almost as surely as chaos. Back in the day of the 1992 Camry, indeed all years before 1996, manufacturers used whatever arbitrary system of self-diagnostic codes they liked. Problematic on its best day, but especially so for codes like Toyota's 55 -- which it didn't bother to list regularly.
In the era of paperclip diagnostics and blinky lights, Toyota's computers could register about 25 different faults; but their code system went to 80 of higher. Part of that disparity is due to the fact that many of those codes meant the same thing, but might show up on different cars, depending on how the computer was programmed. There were two different codes for an intake air temperature sensor fault, two for the vacuum sensor, and four for an ECM failure. That's the case with Code 55 as well. It's the same as codes 52 and 53, translating as a "knock sensor fault." Being OBD-I, that could mean that there was actually a problem with the knock sensor -- which tells the computer if the engine is misfiring or the fuel is detonating -- or is could mean that the knock sensor had detected detonation. If you get Codes 52, 52 or 55 by themselves, the knock sensor is likely bad. If you get them in in conjunction with more serious codes like 25 or 26 for a lean or rich fuel mixture, then you may have fuel detonation in the engine.
