Oki ES3640MFP Service & Troubleshooting Manual page 77

373: Paper Jam
Condition
Paper jam 373 occurs when the paper is inverted for double-sided printing.
1. The DUP-IN2 sensor does not change to OFF-state within the predefined time after the DUP-R sensor changed to ON-state.
The printer stops printing immediately when the jam occurs.
Cause
1. Transport rollers cannot transport paper because they have become dirty with paper dust, toner, etc.
2. A piece of paper, foreign substance, etc., has got stuck in the DUP-IN2 sensor lever.
3. DUP-IN2 sensor motion failure
How to remove the jammed paper
Open the duplex cover - Remove all the sheets that have jammed - Close the duplex cover.
Check Points
Open the duplex unit cover and check the following areas and clean them.