Canon printer B504 error: waste ink tank full fix

When this error hits

You're printing normally on a Canon PIXMA MG3620 or MX490 — maybe you just printed 20 photos for a family album. Then the screen flashes B504 and nothing works. The printer won't print, won't scan, won't do anything but show that error. It's not a paper jam. It's not low ink. It's the waste ink counter.

What's really going on

Every time your Canon printer cleans its print head or purges ink during startup, it dumps the waste ink into a foam pad inside the printer. That pad is called the ink absorber or waste ink pad. Canon tracks how much ink goes into that pad with a counter. When the counter hits a preset limit (usually around 5,000 to 8,000 cleaning cycles), the printer stops and throws B504.

The pad might not actually be soaked. Canon sets the limit low to force you into a service center. On older printers you could replace the pad. On modern all-in-ones like the MG3600 series, the pad is buried and not replaceable without tearing the printer apart. So the real fix is resetting the counter.

What you'll need

• A computer (Windows 7, 8, 10, or 11 — the tool doesn't work on Mac)
• A USB cable. The service tool won't work over Wi-Fi. You must connect the printer directly to the PC.
• The Canon Service Tool v3400 or v3500 (depending on your printer model). Get it from a trusted site — it's not on Canon's official site. I've used v3400 for MG3600 and MX490 series with no issues.

Step-by-step fix

1. Turn off the printer. Press the power button. Wait 10 seconds. Unplug the power cord from the printer. Wait 30 seconds. Plug it back in. Don't turn it on yet.
2. Connect the printer to your PC via USB. Use a good quality cable. Avoid extension cables.
3. Put the printer into Service Mode. Here's how:
   • Hold down the Stop/Reset button (the red triangle or circle with a triangle).
   • While holding that, press and hold the Power button.
   • Keep holding both for 2 seconds.
   • Release the Stop/Reset button but keep holding Power.
   • Press the Stop/Reset button 5 times in a row (while still holding Power).
   • Release the Power button. The printer should light up all LEDs. On some models the screen says "Service Mode". You're in.

   Important: If the printer just turns on normally, you missed the timing. Unplug and try again. I've seen people get it on the third try.

4. Open the Canon Service Tool on your PC. You might need to run it as Administrator (right-click, Run as administrator).
5. Select your printer model from the dropdown at the top. If it's not listed exactly, pick the closest one. For MG3600 you'll often see "MG3600 series".
6. Click "EEPROM" tab. Wait for the tool to read the printer. You should see a list of values.
7. Click "Read" under the EEPROM section. The tool will dump the current counter values. You'll see a field labeled "Waste Ink Counter" or similar. It will show a number like 5000 or 7000.
8. Click "Set" next to that field. Change the value to 0. Click OK.
9. Click "Write". The tool sends the new value to the printer. Wait 10 seconds.
10. Close the tool. Turn off the printer with the power button. Wait 10 seconds. Turn it back on.

After you power it on, the B504 error should be gone. Run a nozzle check or print a test page. It'll work.

If it still fails

• The reset didn't take. Re-enter Service Mode and check the counter. If it still shows a high number, your printer has a hardware lock or the EEPROM is corrupted. Try the tool again with a different version (v3500).
• The pad is actually soaked. If you've reset it twice or three times and the error comes back after a few prints, the foam pad is physically saturated. Ink may leak out the bottom of the printer. Open the printer and check. If there's ink pooling, you need to replace the pad — or more practically, buy a new printer. These budget Canons are designed to be disposable after this point.
• The printer won't enter Service Mode. Try another USB port. Disable any antivirus temporarily. Some modern antivirus blocks the tool's driver access. Also make sure you're using a Windows PC — this tool flat out doesn't work on Mac.
• You don't have the tool. Search for "Canon Service Tool v3400" on reputable forums like FixYourPrinter or YouTube video descriptions. Don't download from random pop-up ads. I've seen fake tools that install malware.

One last thing: after resetting, your printer will stop printing when it hits the limit again. That might be another 5,000 cycles from now. Or it could be 500 if you do a lot of cleaning. Use the printer's built-in cleaning function sparingly. Let it sit idle overnight rather than running three clean cycles back to back. You'll stretch out the life of that pad.