is it yellowing on just the outside fronds or on the new inner growth? Newly planted or established? How is drainage? Last feeding?

Its on the outside fronds. Ive planted 6months ago. The drainage. I do not know how to test the drainage. I havent put any feeding on it. And if it needs feeding. What brand?

Angel, it's not unnormal for sago's to yellow/brown on the outside fronds so they can use that energy for new fronds. Once they turn brown (wait until then) just lop them off. It's important to wait for them to turn brown as the plant is withdrawing the chlorophyll etc back into itself so you don't want to take that away by cutting the frond off too soon. If the insides were yellowing, I'd be more concerned with it needing nutrients. You may have too much standing water and with all the rain we've had in SA, they don't need to be watered right now. They prefer it more dry than soggy. I use blood meal in spring and fish emulsion in fall when I fertilize. I also add a touch of epsom salt. I also add some sand each time so it can work its way in to help drainage. That's just what I do.

Also, do you know what variety it is? Some like gratus and ferox do not like full sun and they will yellow in it.

Others are welcome to give more 'expert' advice :)

I can tell you of my own experience with it. I put it in the ground 3 yrs ago & cover it with several layers of burlap or a couple old king size sheets when temps get below 40ish. But I believe that freezing temps cause the yellow damage on mine. I have several fronds with just little sections yellow, which I eventually cut off. But it growns so well outside that it makes up for it by end of summer. I'm afraid it will outgrow it's spot & the king size sheets in another year or so. LOL.

You might also want to check the underside of the yellowed fronds for scale insects.