HP M476dn Scanner Error 17 driving me insane
Got a bargain HP LaserJet Pro M476dn from an office and it has Scanner Error 17.
The weird thing is the scanner carriage movement itself seems completely normal:
- homes correctly
- moves smoothly
- no grinding/slipping/clicking
- then flashes the CIS light several times near the left/start of the A4 scan area and throws Error 17.
I fully disassembled the flatbed scanner assembly multiple times at this point:
- removed scanner carriage/CIS completely
- checked all FFC cables with a multimeter (continuity good)
- cleaned underside of glass
- cleaned calibration strip
- cleaned CIS slit/window itself (it was visibly dirty)
- checked gears/belt/encoder wheel/etc.
One thing I noticed before cleaning was the scanner illumination MAY have had darker spots / uneven brightness during the calibration flashes, but I'm not 100% sure.
I also tested disconnecting the ADF scanner + motor cables and then the printer throws Scanner Error 16 instead, so it seems like the printer can distinguish the ADF subsystem separately. The visible blinking/error behavior seems to come from the flatbed scanner.
Now for the weirdest part:
After one reassembly attempt it still gave Error 17, so I gave up and printed a CMYK test page. Out of desperation I put the page on the flatbed, rebooted the printer, and suddenly it booted successfully with NO scanner error. Both flatbed + ADF scanning worked perfectly. I removed the paper, rebooted again, still worked.
Then I realized I forgot to reinstall the plastic cable cover underneath the scanner/ADF assembly (the one holding the FFCs + ADF motor cable routing). I partially disassembled it again just to install the cover, put everything back exactly as before, and now Error 17 is back again. CMYK paper trick no longer helps.
At this point I'm wondering:
- CIS module failure?
- FFC/contact issue despite continuity testing good?
- CIS alignment/seating issue?
- formatter/scanner PCB issue?
The annoying part is replacement CIS/scanner parts seem to only exist on AliExpress from China with like 1-2 month shipping, so before I order random parts I figured I'd ask if anyone has seen this exact behavior before. TIA!
