2003 Sedona code P0335B engine stalls

I'm trying to help a lady with a 2003 Sedona. The engine occasionally stalls after warmup, sometimes it starts right back up, Sometimes it takes over an hour before it re-starts. The problem is happening more frequently. It shows a code P0335B CKP Sensor A Circuit Malfunction. Any idea what this is, how to check it, or how to fix it?