i have a 98 civic ex manual and the check engine light it's reading is the vehcle speed sensor. How can you tell that it is not good? Cause the mph is still working.

 

For starters I'd see if the pins are corroded. That's what happened with mine, but my speedometer had stopped working.

 

pull the backup fuse out of your fuse box(7.5 amp on top). leave it out for 30 seconds, then plug back in. This will clear your code. The speed sensor is on the back of the tranny. Remove the 10mm bolt and pry it out with a screw driver. Check for broken teeth, and then check if the plug is clipped into place. My car throws codes for dumb **** all the time. I just remove the backup chip, then everything is back to normal.