Can a dirty encoder strip cause an E4 error on an HP printer?

Yes, a dirty or damaged encoder strip can absolutely cause an E4 error. The encoder strip is a clear, thin plastic strip that the print carriage uses to determine its position. If it's dirty with ink or dust, or if it's damaged, the carriage may not be able to accurately track its movement, leading the printer to detect a 'jam' or 'carriage error' and display E4.