So a couple of days ago i drove my son’s car to go to the other side of town 18mi round trip. The car drove fine there and back. The only thing we notice sometimes is a little hiccup here and there after adding gas because the purge valve needs replacing. He is about to head to worj later that day and backs out of the driveway then shifts to drive to head out and the car wont move. It only moves in reverse. I get a mechanic to come out and scan the obd2. He pulls up these codes:

C1209 rr vss circuit open/short  
C1210 rr vss range performance intermittent  
C2112 valve relay error  
C2402 motor electrical fault  
C1208 LR vss invalid no signal  
C1102 battery voltage low  
C1213 wheel speed frequency error

So due to these he tells me its the two rear speed sensors causing the computer to not know what to do when in drive. I replaced them today and it barely rolls in drive but the roms go up. Still only moves in reverse i took the battery out and charged it. And for some reason the alternator was unplugged which i did plug back then reinstalled the fully charged battery but still nothing nor am i reading any codes with my blue driver scanner. The mechanic told me my transmission fluid was full and good on color as well. Any input would be a great help

2007 hyundai elantra gls 2.0L 138,000 odo automatic.