Cause:
When paper that is about as wide as the paper height sensor feeler is discharged to the shift tray, if it has side face curl, the edge of the paper may fail to go under the paper height sensor feeler and ride up on the feeler; alternatively, by coming in contact with the paper height sensor feeler, it may ride up and press against the feeler and the load from this may hinder the movement of the feeler. In this case, even if the shift tray moves down, the paper height sensor feeler fails to turn the sensor OFF, and the lowering time of the shift tray ends up exceeding 650 ms, and the unit ends up sensing it is full.
This is likely to occur if paper of a certain width is output to the shift tray, the unit may detect being full prematurely. (Paper between roughly 191 mm to 261 mm wide)
Solution: