My question "My car is thunking when going into first gear(it is an automatic) The engine light is on and flashes when idleing" Is it possible that the problem is related and what can I do about it?

I was told that by turning your ignition key on and off in a certain sequence, that different codes would show up so you could diagnose problems with your car. Could anyone tell me how to do this? Thanks!

i receneltly installed a short ram intake for my car, after a while the engine light came on and i got the code read and it said "oxygen too lean"? amyone know how i can fix this? i erased the codes but it still came back after a little while :( help