Konica Minolta 226i/266i/306i C3721 and C3722 Error Code Troubleshooting Guide

Key Takeaways

• C3721 and C3722 are related to abnormal high-temperature detection in the fuser unit.
• C3721 is associated with temperature detection at the center of the fusing roller, while C3722 relates to the edge.
• An error reset can be performed before further troubleshooting.
• If the error returns, inspect the fuser unit, thermistor, wiring, and connectors.
• Allow the fuser to cool completely and disconnect the power before servicing it.

Symptom

A Konica Minolta 266i displays error code C3721 during startup.

Similar fuser-related error codes may also include C3722, depending on the detected temperature condition.

Fault Analysis

The error codes are related to abnormal high-temperature detection in the fuser unit:

The exact cause may be related to the fuser temperature detection system, including the thermistor and its surrounding components.

Troubleshooting Methods

Method 1: Perform an Error Reset

This method can be used to reset the displayed error code before further hardware inspection.

Step 1: Enter the Error Reset Menu

Power on the machine while holding the Reset button.

A small black dot should appear in the top-left corner of the screen. After a short wait, the machine should enter the error reset interface, as shown in the image below.

Step 2: Reset the Error

Tap Error Reset.

When OK appears at the bottom of the screen, confirm the reset.

Then power the machine off and back on again to check whether the error code has cleared.

Important: If C3721 or C3722 returns after the reset, further inspection of the fuser unit may be required. An error reset does not necessarily correct the underlying hardware problem.

Method 2: Inspect and Clean the Fuser Thermistor

If the error returns after the reset, inspect the fuser unit and thermistor.

Safety Warning: The fuser unit operates at high temperature. Allow the machine to cool completely and disconnect the power before removing or servicing the fuser unit. If you are not trained to service copier hardware, consult a qualified technician.

Step 1: Turn Off and Unplug the Machine

Power off the machine and disconnect the power cord.

Allow the machine to cool sufficiently before working around the fuser unit.

Warning: The fuser unit can become extremely hot during operation. Make sure it has cooled down before removal.

Step 2: Remove the Rear Cover

Remove the screws securing the rear cover, as shown in the image below.

Step 3: Disconnect the Fuser Connectors

Disconnect the four connectors connected to the fuser unit.

Route the cables out of the way to facilitate removal of the fuser unit.

Step 4: Remove the Fuser Unit

Open the side cover and remove the four screws securing the fuser unit—two at the top and two at the bottom, as shown in the image below.

Step 5: Remove the Fuser Unit

Carefully remove the fuser unit from the machine.

Caution: Make sure the fuser has cooled completely before handling it to avoid burns.

Step 6: Access the Thermistor

Remove the two screws securing the paper guide plate that holds the separation claws.

Route the sensor and thermistor cables out of the way, then remove the guide plate to access the relevant components.

Step 7: Clean and Reinstall the Thermistor

Inspect the thermistor for toner contamination, dirt, or other visible abnormalities.

Clean the thermistor as appropriate and reinstall it.

Then reinstall the fuser unit and reconnect all cable connectors.

Step 8: Perform the Error Reset Again

After reinstalling the fuser components, access the error reset interface again.

Power on the machine while holding the Reset button and wait for the small black dot to appear in the top-left corner.

Enter the error reset menu, perform the reset, and confirm OK.

Then power the machine off and back on again to check whether the error has cleared.

Important: C3721 and C3722 are related to abnormal fuser temperature detection. If the error returns after an error reset and thermistor cleaning, the fuser unit, thermistor, wiring, connectors, and related temperature-control components may require further inspection or replacement. The exact troubleshooting procedure may vary by model and firmware.

FAQ

What does Konica Minolta C3721 mean?

Konica Minolta C3721 indicates abnormal high-temperature detection in the fuser unit, specifically at the center of the fusing roller. The issue may be related to the thermistor, wiring, connectors, or other fuser temperature-control components.

What is the difference between C3721 and C3722?

C3721 is associated with abnormal high-temperature detection at the center of the fusing roller, while C3722 is associated with abnormal high-temperature detection at the edge of the fusing roller. Both error codes are related to fuser temperature detection.

How do I reset a Konica Minolta C3721 error?

On applicable models, power on the machine while holding the Reset button. Wait for the small black dot to appear in the top-left corner, then enter the error reset interface and select Error Reset. Confirm OK, then power the machine off and back on again.

If the error returns, further troubleshooting of the fuser unit may be required.

Why does C3721 return after an error reset?

An error reset may clear the displayed error temporarily, but it does not necessarily correct the underlying cause. If C3721 returns, inspect the fuser unit, thermistor, wiring, connectors, and related temperature-detection components.

What should I check if C3721 keeps returning?

First, make sure the machine has cooled completely and disconnect the power before servicing the fuser. Then inspect the thermistor and its surrounding components, including wiring and connectors. Cleaning the thermistor may resolve contamination-related detection problems.

If C3721 continues to return after inspection and cleaning, the fuser unit or related temperature-control components may require further testing or replacement by a qualified technician.

Conclusion

Konica Minolta C3721 and C3722 are fuser-related error codes associated with abnormal high-temperature detection. An error reset may clear the displayed code, but if the error returns, further inspection of the fuser unit, thermistor, wiring, and connectors may be necessary.

Before servicing the fuser unit, always allow it to cool completely and disconnect the power. If cleaning or basic inspection does not resolve the problem, further diagnosis or component replacement by a qualified technician may be required.