2010 Hyundai Accent Speed Sensor

Recently I purchased a used 2010
Hyundai Accent GLS. Certified but it
needed a little work .. mainly the front
right wheel baring and front left ball
joint, they also fixed a broken seal on
the transmission and an O2 Sensor.
Everything was good driving home
until I was backing up in my driveway
and the check engine light came on. I
believe the code is P0501, it's the
Speed Sensor! So they had to order it
from a dealership, a week later
installed it. Everything was good, until
about an hour and half later the check
engine came back on, hooked it up
to.a reader and sure enough it's the
Speed Sensor. Now the mechanic
wants to send my car into the
dealership for a fee days so they can
determine what the problem is.

So here are my questions;
1. The work they did on the front end,
could that have caused the sensor to
malfunction.
2. Does this failed sensor, would it
cause horrible gas consumption
because I'm only getting about 400-
450 km per tank!!
3. Is this a common problem with this
particular car and if so what is the
solution . Like I said, the sensor has
been replaced already so will I have to
keep replacing it cuz the warranty will
expire soon and cost is pretty high!

Any assistance would be greatly
appreciated. Thank you in advance!