Conflict of polarity?
R2 constitutes the lower half of a voltage divider used to reduce out-of-range voltages to potentials sample-able within the range of an MCU input rating.

Voltage dividers do not change polarity relative to their fixed ground.  This circuit accepts a positive input, and yields a reduced positive output.

However vehicle electrical systems are notoriously nasty, and it is a legitimate question if this design overall is sufficiently robust for such usage.