[Error Code] Canon Fax Machine 8500 - Check Printer Cover Message - Need Parts Manual

[ignacio.cortez]

I have a client with a Canon Fax Machine 8500 that has a message saying:

Check Printer Cover, I've reseated all the covers, cleaned the sensors I had
access to, even tried a new Toner Cartridge, I still get the same error.

Anyone knows, in these models, which is the Printer Cover, and also, (I have
a feeling is a bad sensor) what sensor is and what is the part number?

I need to give the client an estimate ASAP. Any help?