Here's a blast from the past: Google's new phone is having trouble pairing or staying connected to Bluetooth in many cars. In 2015 we went through this with the Nexus phones on Marshmallow, and this year it's the Pixel with 7.1. Google is aware of the issue, and is actively investigating.

Pixel owners are reporting a few variations of connectivity issues with their cars. Some people are able to connect quickly and stream audio, but calls fail and Bluetooth disconnects. Others are able to connect with some difficulty, but the device will drop off for no apparent reason. A few also mention Nexus phones on the 7.1 preview are doing similar things, so perhaps this is a bug in the new build of Nougat. It does not appear to be limited to a certain vehicle, but problems with GM seem more common.

Whatever the cause, Google has started reaching out to people who have reported the issue via the Pixel support community. It might be a while before an update is deployed to resolve this issue, but at least Google can push it out directly to its phones.

Source: Pixel Community

Thanks: John and Andrew