Where is main control unit on 1995 Nissan Maxima?

It is located in the console (under the radio). It is accessed by taking off the cover by the accelerator. The ECM can be controlled by a screw (which may be behind some tape) on the left of the device. Turn clockwise and hold for two seconds. Turn screw back to the original position. The engine light will now blink the appropriate codes repeatedly. Count the slow blinks followed by the fast blinks. So "blink --- blink ------- blink-blink-blink" would be read as 2-3.

The codes will repeat until the car is started. So, there is no rush to check the counts after you turn the screw.