ok i got a code today on my 94 4x4 w blazer. Its a 42 DTC - 42 Ignition bypass circuit error Can anyone tell me what this means?

 

I dont remember exactly what it is but i had the same code on my 91. My son (mechanic) said check knock sensor or bad tank of gas so i did change back to my regular gas station, and next day code went away (still stored in computor) but check engine light went off. it turns out bad gas will throw a code 42