what is the manufacturer code P 1506 on 1996 Mazda B2300

I have change the o2 sensor and the air control valve, It will not pass emmissions inspection. What do i do.

Asked by for the 1996 Mazda B2300
The Check Engine light is a yellow light on the dash which should illuminate when the ignition key is turned on and go out a second after the engine starts. It is usually a yellow outline of an engine, some car manufactures make it confusing and just have the words "Service Engine Soon"