How to solve error 6A90 or "APP sensor error" on Canon printers

Error code 6A90 or "APP sensor error" occured during paper feeding or purging.

Solution 1:

• check for foreign material or paper debris around the purge drive system unit;
  - remove foreign material.

Solution 2:

• check for foreign material or paper debris around the ASF unit;
  - remove foreign material.

Solution 3:

• If other solution fail, replace one off the following part

- Purge drive system unit
- Logic board

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