Issue Description:
Poor black transfer seen with larger fonts or areas of large toner coverage.
Solution:
Step 1:

If available, update code to FW5.2, or later.

Retest.

If the issue is not resolved, proceed to step 2.
Step 2: Perform a re-calibration.

Activate by navigating to Settings > Print > Quality > Advanced Imaging > Color Adjust > Start.
Click here
to see the steps illustrated.

Retest.

If the issue is not resolved, proceed to step 3.
Step 3: Increase toner darkness setting.

To do this from the control panel, navigate to
Settings >
Print Settings >
Quality Menu >
Toner Darkness.

Retest.

Still Need Help?
Have the following available when calling Lexmark Technical Support;
Printer model(s)
Printer serial number
Toner/imaging unit/waste toner bottle part number and serial number
Note:
Please provide this article ID# SO8624 for reference.
LEGACY ID: SO8624