99 maximum service engine soon light

Hi Guys,

I got a 99 maximum. The service engine soon light came on and off several times. It came on again last month.I followed the instruction below: the Check Engine light at:

The code is 0505 which means nothing is wrong. Now, I took it to the state emission test, the machine complains that several sensors are not available such as O2. I don't know if I did anything wrong or not. The light went off right after I did the diagnosis (without doing the procedure of dismissing the light, i.e. repeating the same thing three times in a row). I did turn the screw counter-clock wise until it reach the stop.

Any ideas?

Thanks, Ivan