When someone calls us about a patchy lawn in Sunnyvale or Mountain View, the first thing we do is not look at the grass. We run every zone and stand there watching it, because more often than not the grass is fine and the water is not arriving.
Do the same thing yourself before you spend money on sod. Turn on one zone at a time in daylight and walk it. You are looking for heads that have sunk below the grass line, heads spraying the fence or the driveway instead of the lawn, heads that have been knocked out of alignment by a mower, and areas where two heads do not overlap. Sprinklers are designed for head-to-head coverage, meaning each head's spray should reach the next one. Where that overlap is missing, you get exactly the kind of dry patch people mistake for a disease.
The second common fault is zone mixing. If one valve waters lawn and planting beds together, one of them is always getting the wrong amount. Lawn wants shorter, more frequent cycles; established shrubs want longer, deeper, less frequent ones. Run them on the same zone and you either drown the shrubs or starve the grass.
The third is the controller. We regularly find systems still running a July schedule in December, or a schedule someone set five years ago and never revisited. A smart controller that adjusts to weather solves this permanently and pays for itself quickly at California water rates.
A zone audit and a handful of repairs is a fraction of the cost of a new lawn, and if the coverage is the problem, new sod over the same broken system will look exactly the same by next August. Fix the water first, then decide whether the grass actually needs replacing.