Does PCM retard timing?

Just a quick question… I’ve heard that when your Service Engine Soon light is on, it retards the timing. Is this true? My lights been on for the past few months and I took it to the dealership yesterday and they said the catalytic converters are burned up, so they’re ordering new ones. Under what circumstances would the PCM retard the timing?
Thanks
Chris

The only time I know of that the pcm retards timing is when you get knock.