Rabbi Yisroel Reisman spoke about this one year before Pesach. He used a special industrial thermometer to test the temperature of various ovens on Self Clean mode.
Whereas the old ovens used to get to 900 degrees, which is certainly enough, many of the newer ones DO NOT reach that high. Some of them only got to 700 degrees, which is NOT enough for Libun Gamer.
Footnote – he also tested the temperature right at the gas burner, and actually broke the thermometer. It was MUCH higher than even a self-cleaning oven. Maybe around 1400 degrees! So another option for the Cast Iron pan is to put it on the burner (or across two burners) and keep rotating it every 12 minutes or so until every inch of it (top and bottom) has become red hot for a moment. Unlike a Mikvah, kashering can be done an inch at a time. Make sure you use pliers or heat-proof gloves to move the pan around. This can cause very bad burns.
I don’t have a self-cleaning oven, and I have kashered pans and stove grates this way many times. More recently though I just ask my neighbor if I can add my grates into their oven when they self-clean it.