The Earth is moving too..............
Thanks for your interest.
Earth's motion is built in to the Horizons App. Voyager I is moving away from the sun at about 16 km/sec. On the date and time specified, the earth's orbit is on the far side of the sun from Voyager. The earth's orbital velocity is about 30 km/sec. The "vector sum" of earth's velocity and Voyagers is about between 25.4071922 and 25.1404967 km/sec on the first and last date in the day posted. The corresponding heliocentric range rates are 16.8815689 and 16.8815679 km/sec.
Voyager will not be one lightday from the sun until 2027-Feb-04 11:58:39.327