Open door B and remove the toner cartridges by pressing the four green buttons for each color.
Open the lower side cover by pressing the C-labeled blue button and remove the waste toner bottle.
Lift the blue levers to unlatch the imaging unit basket, then remove it.
Note: Set the imaging unit on a flat and level surface.
Open the front door A. Push the gray finger tab to unlatch the transfer module and carefully pull it out.
Press the second toner contact for the transfer module.
Did the contact spring back into place?
Reinstall the transfer module and close front door A.
Reinstall the imaging unit and make sure that the two blue latch levers are in the full down position. Reinstall the toner cartridges and close the C blue button and upper cover B. Run a few print jobs to see if the performance improves.