The printer displays a "Fatal Error - 140 Contact Service". The error codes can range from 140, 141, & 142.
This error indicates that the Image Drum Up/Down Process is not working properly.
The errors are as follows:
140 - Yellow Drum Up/Down error
141 - Magenta Drum Up/Down error
142 - Cyan Drum Up/Down error
1. Reseat the Image Drums. Ensure they are in seating properly into the drum carriage.
2. Reseat the Toner Cartridges. Ensure they are seating properly into the Image Drums.
3. Reseat the Contact Sensor Spring assembly and inspect it for damage or mis-alignment. If the springs appear bent or dis-lodged reseat them.
4. Try a new Transfer Belt.
Source: Oki knowledge base