Elected officials and transit watchdogs are calling for a full accounting of an MTA boondoggle that has cost taxpayers $530 million — but still isn’t all systems go.

A new data network for the subways is hundreds of millions of dollars over budget and years late.

Begun in 2000, the SONET fiber-optic network was supposed to equip the subways with security cameras, digital train-arrival boards, more PA systems and a centralized way to monitor trains.

But the work hit serious snags, including computer servers frying in subway storage rooms, fiber-optic cables breaking, and network batteries exploding.