I've recently purchased a '97 Tercel and have some questions about maintenance. First off, I'm automobile illiterate and will probably ask some foolish questions so please bear with me. Recently, while driving to work, the check engine light came on. I checked the oil & it was a little low. I topped it off but the light is still on. Next I started to check the transmission fluid but can't find where to do so. Am I able to check the transmission fluid or do I have to take it to a dealer? Would an auto part store's diagnostic test accomplish the same thing as a dealers tests? I checked the differential fluid and it was a little low, could this be related? Any other suggestions on what to check would also be appreciated. Thanks for any help.
Weird

The check engine light are related to emission issues. So, checking fluid levels like oil and automatic transmission fluid will not help to find the causes. You will need a OBDII scan tool like ScanGauge (http://www.autodax.com/catalog/pdetail.php?prdid=226) and attach it to the OBDII port in your car to retrieve the error code(s).

Have you noticed if your Tercel has been loosing engine performance like drop in gas mileage, rough idle, difficult to start in cold morning, etc? The causes might lie in faulty O2 sensor located on the exhaust pipe, clogged EGR valve, faulty EGR control module, vacume leak from the cracks of the aging rubber hoses, etc. You will need to bring your Tercel to a mechanic to find the true cause(s). Even the error code(s) from a scan tool may not pinpoint the exact cause(s). For example, if the error code indicates a faulty O2 sensor, the real cause may not be the O2 sensor itself, but something else that causes the O2 sensor to give false reading. These emission related parts are expensive to replace. Please find a honest mechanic to look into it.

Just my 2 cents.