Image forming apparatus executing maintenance mode for diagnosing cleaning member

An image forming apparatus comprising:

• a photosensitive drum configured to carry toner;
• a developing roller configured to supply the photosensitive drum with the toner;
• a transferring unit in contact with the photosensitive drum at a transferring nip, the transferring unit being configured to transfer a toner image from the photosensitive drum to a sheet at the transferring nip;
• a cleaning roller in contact with the photosensitive drum to form a collection nip, the cleaning roller being configured to collect toner from the photosensitive drum at the collection nip;
• a circuit configured to apply to the cleaning roller a cleaning voltage prompting the cleaning roller to collect toner;
• a supply mechanism configured to start feeding a sheet to the transferring nip;
• and
• a controller configured to execute a maintenance mode in which the controller is configured to execute:
• after the developing roller supplies a predetermined region of the photosensitive drum with toner, i) controlling the circuit to maintain a state where the circuit does not apply a voltage having a polarity opposite to toner to the transferring unit while the predetermined region of the photosensitive drum passes the transfer nip;
• after executing the controlling i), ii) controlling the circuit to apply to the cleaning roller the cleaning voltage having a polarity opposite to toner while the predetermined region of the photosensitive drum passes the collection nip;
• after executing the controlling ii), iii) controlling the supply mechanism to start feeding a sheet toward the transferring nip;
• and
• after executing the controlling iii), iv) controlling the circuit to apply a voltage having a polarity opposite to the toner to the transferring unit while the predetermined region of the photosensitive drum passes the transferring nip.