Does it show signal levels (S/N) of between 6 and 20?

the higher the number the better
Typical is to have 4 to 5 satellites with >7, and from that group, often 2 or so at around 15

If your signal levels are about 0...3 then the antenna is bad

It is rare to have all 8 channels see a satellite.

Also, Almanac should be OK
Gyro should be 2500 +/-100 when sitting still, and increase when turning one direction, and decrease in the other
Wheel sensor should show wheel pulses: positive for forwards, negative for backwards, and change according to speed
Direction of travel must be forwards in all gears except when in Reverse.

If any of these inputs is not working, it'll affect the accuracy of the nav