Yesterday I took my 94 GXE to Midas because my "check engine"light was on, they said there is problem with O2 sensor/circuit.

Today I made a phonecall to dealer, they charge $170 for checking which one out of the 3 o2 sensors is bad. It's too much!

So can anyone tell me where are they and can I replace it by myself?

Other thing: my coolant is low. Can I add some to the plastic bottle myself? What is the number of that blue liquid?