I was unclear in my question. Here's what I meant to say:

How long do fault codes stay in the computer if they are not manually cleared?

I had understood that the computer itself has the capacity to clear certain codes if a certain number of normal operation cycles (i.e., engine start/stop) occur, so that a one-time, transient fault code won't stay resident in the computer forever.

Is this accurate?

__________________
Steve
'93 400E