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If there is a blockage in the paper feed system, the printer will be unable to feed in any fresh paper and will "think" there is no paper in the paper tray.
Did any sheets of paper recently get stuck inside the machine? If so, there may be a small fragment of paper still stuck inside it which is preventing any fresh sheets of paper from getting fed in.
Have a look and check for any obvious blockages or small pieces of paper that may be causing the jam.
If you can't see anything, then try to remove any obstructions by manually pushing a piece of thin stiff card through the machine, where the paper normally goes through.
Let me know if that helps?
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Have you pushed a piece of thin stiff card all the way through the machine to ensure it is free of blockages?
If so, then the next likely cause of the problem is a faulty paper jam sensor.
You can test the sensor for continuity using a multimeter and replace it once confirmed as faulty.
The paper jam sensor is deep within the machine and will require disassembling the entire printer. It is not an easy fit.
Normally Canon will simply replace a printer with a fault rather than attempt a repair since it is so labour-intensive.
The sensor will show closed circuit if it is faulty since it is permanently activated.