Unfortunately the User Manual doesn't provide details for "168D". Did the printer also show an error message alongside that code?
Nearby codes (e.g. 1686 through 1688) all deal with issues with the ink cartridges. See pages 348 through 350. Perhaps 168D would be similar.
You probably should call up Canon though to see if they have documentation on that specific code.
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Ricky
Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers
