Could've fooled me. You were stupid enough to:
1) title your post "how do I clear code 51".
2 jump on the guy who told you how based on that wording.
3) then admit you know how to clear it which is what your original question was.
4) not search for the answers you seek which have been posted here many times in the recent past.
5) neither own a TSRM nor read the online one, which the guy who tried
to help pointed you too.
I guess we're all supposed to be mind readers in your case. OK, fair nuff. Since I know the exact answer to your questions (and your problem) see if you can read mine.
....oops, looks like the others beat me to it.