Check Engine Light on 2006 Suzuki Forenza

Check engine light comes on and car will lose some power climbing a steep grade. The light does not blink. It will eventually go off by itself, it may be a few hours or the next day. The light may not come back on for days or a week or more. Any suggestions on what this could be? Thank you.

Asked by for the 2006 Suzuki Forenza
you need to have a diag to see what the code is and why the failure occured.