How To Prevent a 1240 Error During Printing

If you’ve got a Canon printer with an operational panel (you know, the one with buttons and that little LCD screen), chances are you’ve run into the 1240 error at some point. It’s kind of a pain, especially if you’re trying to print quickly and suddenly the printer just throws this error at you. Canon suggests a pretty straightforward fix, which is lifting the operational panel and pulling out the output tray while printing. Not doing that can sometimes trigger the error, so make sure you’re following that or else it keeps bugging you.

Most of the time, this error can be cleared just by following what pops up on the screen—lift the panel, pull out the tray, and the error should disappear. If not, some folks have had success bypassing the detection sensor that checks if the panel is closed. Not exactly a perfect fix, but hey, sometimes you just want to get printing without messing around with hardware—especially if the sensor is faulty or clogged.

How to Try Fixing the 1240 Error on your Canon Printer

Follow the instructions on the printer screen

This is the obvious first move, because it usually works. When you see the error, check if the message suggests lifting the operational panel or pulling out the output tray. Usually, the printer will guide you pretty clearly. So here’s what to do (and yeah, it sounds simple, but it works on many setups):

• Make sure the printer is still powered on. Grab the operational panel and lift it up until it’s parallel to the body. On some models, you’ll hear a click—that’s the panel locking into place.
• Pull the output tray out all the way. Don’t stop partway—if you don’t fully extend it, you might see a different error like “1259 output tray error.”
• Lift the paper support on the edge of that output tray. You know, the little plastic thing that holds the paper in place.
• Extend the support extension too, for good measure.
• Tap OK on the printer screen. Usually, the error will clear, or at least the screen will ask you to confirm that you’ve done the steps.
• If the error sticks around, try turning the printer off and on again, then repeat the process. Sometimes, a reboot helps reset whatever’s stuck.

Clean the sensor – it might just be dusty or blocked

A little known thing is that inside the printer, just below the operational panel, there’s a tiny sensor—usually a small white plastic lever—that detects whether the panel is open or closed. If this sensor gets covered in dust or paper debris, it can fool the printer into thinking the panel isn’t correctly set, triggering the 1240 error even if everything appears fine.

So, here’s the trick: power down the printer, open that operational panel, and look for the sensor. It’s usually on the left side, a small white lever. Lightly clean it with a soft lint-free cloth. No need to go crazy—just enough to remove dust or grime that might be blocking its movement. Also, move the panel up and down a few times to see if the sensor moves freely. If it feels stiff or stuck, that might be your culprit.

After cleaning, close everything up, restart the printer, and see if the error is gone. I’ve had cases where this simple wipe cleared the false error even if the panel looked fine, so it’s worth a shot.

Removing the sensor to bypass the error — a last resort

Alright, if everything else failed, some people have tried physically removing the sensor as a way to bypass the error, especially if they suspect the sensor is broken. This is kind of the ultima ratio—stuff like this can void the warranty or cause other issues, so proceed with caution and only if you’re comfortable with small hardware mods.

Here’s the gist: lift the operational panel, find that tiny sensor lever, and gently use an X-Acto knife or a small household knife to detach it from the printer. Be super careful not to scratch anything or hurt your fingers. Once it’s off, close the panel, press OK on the screen, and see if the printer now considers the panel closed. This trick tricks the printer into thinking the panel is always closed, so it won’t throw that error anymore.

Caution: doing this is at your own risk, and you shouldn’t use thick paper or do heavy printing afterward. It might cause paper jams or damage your printer, and definitely void any warranty you have left. Still, on some setups, it’s the only way to get around the constant error if the sensor’s wonky or broken.

And yeah, if none of this works or it seems complicated, don’t sweat it—contact a legit printer repair tech or reach out to Canon Support. Sometimes, the fix is a sensor replacement or something else requiring professional hands.