2000 Blazer.Does anyone know what causes this code? My wife called me and said that the check engine light was on and the truck was running rough. When I got there the truck was running fine. I checked the codes with a code reader and code PO305 came up(misfire on cylinder 5). I erased the codes and all is fine.

 

You may have had a loose plug wire or a gummy plug. Check the wires first.

 

P0305 is a missfire on #5 spark plug. Like pointed out above, check the plug and wires to #5 first.