I have tooth sensitivity on tooth 14, upper left side. I had a root canal done and a crown. What’s wrong with the tooth?

Usually when a root canal
treated tooth has sensitivity, the tooth may be a little too hard in certain
movements. I would have your dentist evaluate your “bite” on this tooth
and adjust as necessary. Have them take an x-ray to ensure that there isn’t
something going on at the root of the tooth. On occasion, a tooth may
have an extra root or chamber that may have been missed with the original root
canal.

If you have had a successful root canal treatment on this tooth then this is not the source of the sensitivity.  If the crown was a full coverage crown then it is unlikely that the you are feeling sensitivity from a fractured cusp.  It is possible that the root is fractured and you feel it when biting in a certain position.  Sometimes these fracture lines are so small that they are not evident on a radiograph.  If the sensitivity is ongoing then you may want to go back to the endodontist and have them check for a fracture in the root.  To add to this on occasion you can get referred pain meaning the problem is not tooth # 14 but is referred from another site.