The majority of cars made after 1996 use the OBD-1 or OBD-2 code system to notify owners of problems with the car's engines or sensors. A 1992 Lexus SC400 has the same capability to report OBD (on board diagnostic computer) warnings but uses neither of these code systems. To reset the OBD codes on a 1992 Lexus SC400 you can take it to the dealer or do it yourself in a few simple steps.
Park your 1992 Lexus SC400 on a level surface. Turn off the engine. Engage the parking brake and open the engine hood.
Disconnect the negative cable from the battery, using a wrench to loosen the retaining bolt holding the cable clamp onto the battery post. Pull the cable away from the battery and make sure it cannot touch any metal.
Turn on your headlight switch. You don't have to start the car; just flip the switch on and leave it in the on position for 10 minutes.
Turn the headlight switch to the off position and reconnect the battery.
Drive your Lexus for at least 45 minutes, allowing it to move through all of its gears. Since you have just reset the codes, you have zeroed out the computer. You must allow it to reprogram itself to manage the transmission. You may have to reset your clock and radio settings as well.
