canon pixma paper jam error

[marts_8]

im using pixma mx328 all-in-one printer. i turned-on the printer, print 3 pages then it suddenly said paper jam error but the paper was not even stuck a bit, it came out clean. after flashing that error, i heard a different loud sound in the right part. i pressed ok and still error. i turned it off and on and still error but now it is making a weird sound like a rubber was in between the gears.

i have managed to take it apart today but don't know where to look to check where the error came from.

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i think i know the error. there is a black plastic thing in the middle of the sensor. is my diagnosis correct?

 

[marts_8]

the above pic is the normal position. I put back the unit to test it out. i power on the printer and there was no paper jam error. i put in a paper to print. the paper rolled in but did not even went through the ink carriage. the big grey rubber roller just didn't continue rolling and paper jam error occurred. what you think is wrong? is it the paper feeder motor?