A large vertical band of toner appears on one side of the page. The dark band will not be perfectly vertical, although it might appear to have some pattern to it as it goes down the page. The dark band will have a gradient from black to white and have a fuzzy haziness to it. The line will be from one page edge inwards towards the middle of the sheet.
The left side of the page is dark and illegible.
The right side of the page is dark and illegible.
If the print defect appeared only after replacing the Imaging Unit, a piece of the shipping separator may have broken off into the Imaging Unit while being removed. In such a case, the charge roll(s) will not be in contact with the Photoconductor drum, thus causing the dark print.
Should the defect persist or if no plastic or other obstructions are found inside, please contact Lexmark Support for other troubleshooting suggestions.