Most likely, the failure is from the transfer system where no voltage is being applied to the transfer roller; thus, inspection of the system from high voltage power supply (HVPS) to the transfer roller must be done. Following these steps below will guide you in troubleshooting the print quality defect.
If the issue happens after installing a new maintenance kit, check whether the transfer roller included with the kit has been installed in the printer. If necessary, replace the Transfer roller (part number: 40X7582)
Should issue occur immediately after the printer has been serviced, the connector may have been removed and not reinserted into the HVPS.
Please remove the printer's right-hand cover and verify that the pink/red cable found on the lower right-hand side of the HVPS is properly installed. Also remove the transfer roller and ensure that the bronze bushing found in the left transfer bracket is still present.
Replace HVPS (part number: 40X7578) if necessary.
Clean any of the contacts as needed (ensuring the printer is powered off and unplugged before doing so).
Check whether the pink/red transfer cable is pinched in the housing. If cable is damaged, replace the Transfer arm with cable (part number: 40X7605).
Should there be additional concerns or questions, contact the next level of support for further diagnosis.