How do I test to see if my alternator is bad? The dashboard lights: Gas, batt, and brake light all came on randomly. Theyll go off at 2500 RPM and my volt meter reads somewhere in the 9 volts range.

Most auto parts stores and auto electric service locations will test it for you, free of charge. Generally, if the battery voltage does not increase with a small increase in RPM, you probably have a regulator or alternator problem. Most modern alternators have the regulator built in. You may perhaps have a computer issue, but further tests are probably beyond your ability. You've tested most things one can easily test. Again... an auto parts store will test it, usually free.

9 volts isn't enough my friend. You need about 14 to14.5 at a fast idle. Get a hand held automotive volt meter/tester and put the two clips on the two battery posts. Read the voltage without the engine running. Then start up and read the voltage at 2500 rpm. If the voltage is 12-13 at idle and 14 or so at 2500 then the gauge is faulty. If the volts are barely different to the static voltage or lower then the alternator is basically dead. The vehicle systems may play up when the volts fall below a certain level. I can't comment on the 02 sensor but that may be an independent fault. Some alternators have replaceable brushes or regulators complete with brushes. If you are handy with tools download some info on swapping the brushes/regulator or consult the workshop manual because the brushes are a few bucks and half an hour to change. If the alt has done a high mileage there will be wear on other components, bearings etc and a replacement would be a better long term bet. Check out your local parts store or go online to a Japanese auto spares site.