DETROIT — Waymo, Google’s self-driving car division, will start testing its new fleet of minivans on public roads in California and Arizona later this month.

The minivans, built in collaboration with Fiat Chrysler, are Chrysler Pacifica hybrids outfitted with Waymo’s own suite of sensors and radar. Waymo and FCA announced their partnership in May.

In a speech at the Detroit auto show Sunday, CEO John Krafcik revealed that Waymo built the sensors, radar and software for the new minivans itself.

Krafcik said the company felt the system would work better if it was developed specifically for self-driving instead of using off-the-shelf parts.

Waymo, which has been developing self-driving cars for eight years, expects to reach 3 million miles of test-driving this May, Krafcik said.