So, my brother and I have had some problems with his 95 240sx for a while now. My question isn't so much about how we are fixing it, but more with the check engine light. We had checked the codes, 4 came up, one being the mass air flow sensor. We then decided to reset the codes. While the car was running, he unplugged the MAFS and no engine light came on whatsoever. With the car still running, he plugged it back in....still no light. We shut it off, then back on, took it for a drive came back, and yet now light had shown up. Does anyone know if the car has to go through cycles before it will throw up a code...like a reoccurring problem? Is that why the light isn't poppin up, or what?