Epson WF-3640 "Close Scanner Unit" Error Fixed but Ink Cartridge Won't Move - What to Do Next

Customer Question:
After watching your video about fixing the Epson WF-3640 "Close Scanner Unit" error, I tried placing a small eraser on the sensor, and that successfully cleared the error. However, now the ink cartridge carriage won't move or release, so I can't replace the cartridges. What should I do to fix this?

Answer:

Understanding the Problem

The "Close Scanner Unit" error on the Epson WF-3640 is triggered by a mechanical push switch sensor located near the scanner lid hinge. When the printer thinks the scanner unit is open, it locks most operations-including moving the printhead carriage.

By placing an eraser on the sensor, you essentially forced the switch into a "closed" state, which cleared the error. That part worked-but it may now be interfering with normal operation.

Why the Cartridge Carrier Won't Move

Even though the error message is gone, the printer still controls carriage movement based on internal logic and sensor feedback. Here are the most likely causes:

1. Sensor Is Over-Pressed or Misaligned

If the eraser is too large or pressing too hard, the switch may be stuck in an abnormal position. This can confuse the firmware, preventing the printer from initiating carriage movement.

2. Printer Is Not Properly Initializing

After clearing an error manually, the printer may require a full power cycle to reset its internal state. Without that, the carriage may remain locked.

3. Carriage Lock Mechanism Still Engaged

Epson printers often lock the carriage when powered off or when an error is active. If the system didn't fully reset, the lock may still be engaged.

4. Firmware Safety Behavior

Even if the sensor is "tricked," the printer may still detect inconsistency and refuse to move the carriage as a safety precaution.

Recommended Fixes

Step 1: Remove the Eraser

Start by removing the eraser completely. Since the scanner sensor is just a simple push switch, using an eraser is only a temporary workaround and can create new issues like this.

Step 2: Manually Test the Switch

With the scanner unit open, locate the switch and press it gently with your finger. You should feel a small click. This confirms it's working properly.

Step 3: Power Reset the Printer

1. Turn the printer off

2. Unplug it from power for 5-10 minutes

3. Plug it back in and turn it on

This helps clear any lingering internal lock states.

Step 4: Try Proper Lid Closure

Close the scanner unit firmly and ensure it is seated correctly. Sometimes the issue is simply alignment rather than the switch itself.

Step 5: Attempt Carriage Release

Once powered on:

• Open the cartridge access door normally

• Wait to see if the carriage moves automatically

If it doesn't, try turning the printer on while the scanner unit is properly closed (without the eraser).

Alternative Fix (Advanced)

If the switch is faulty or unreliable, a more permanent solution is to re-wire or bypass the switch properly. This involves connecting the switch wires so the printer always detects a closed state-without using physical pressure like an eraser.

However, this requires disassembly and should only be done if you're comfortable working with internal components.

Important Note on Error Behavior

Even though your original issue didn't display a numeric code, the "Close Scanner Unit" error acts like a system-level lock. When triggered, it prevents:

• Printhead movement

• Ink cartridge replacement

• Printing operations

So, even partial fixes can leave the printer in a semi-locked state if not handled correctly.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. So, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We do offer an in-person evaluation and repair service via our local diagnostic facility (https://bchtechnologies.com/printer-repair-service [https://bchtechnologies.com/printer-repair-service]). Given the high demand, we operate on a first-come, first-served basis, and it may take a few weeks before we can accept new drop-offs. Our services are structured to repair either a complete printer or specific components, with clear guidance throughout the process. That said, we understand our rates may not be the most budget-friendly, so we strongly encourage exploring self-help options first. A great place to start is YouTube, including our channel homepage (https://youtube.com/@bchtechnologies [https://youtube.com/@bchtechnologies]). Use the search icon near the "About" section to find videos related to your issue. With hundreds of videos created over the years, this is the fastest way to locate relevant content-and YouTube may also suggest helpful videos from other creators.

Thanks again for reaching out and for trying the fix from our video. You're very close to resolving this-just a matter of getting that sensor behavior back to normal.