31

How to Fix It

1. Open the printer's top cover or front access panel and look inside the toner cartridge area. Check whether a cartridge is actually installed. If the slot is empty, install the correct toner cartridge.

   This seems obvious, but it is worth confirming. Error 31 always means 'no cartridge detected' from the printer's perspective.

2. If a cartridge is installed, remove it completely and reinsert it. Push it firmly until it clicks or seats securely in place. A partially inserted cartridge does not make full contact with the electrical contacts.

   On HP LaserJet 5L and 6L models, the cartridge slides in from the front. Ensure the cartridge is pushed all the way in until you feel resistance — it should sit flush with the front of the printer.

3. Inspect the electrical contacts inside the printer's toner bay — small metal pads or pins. Also check the contacts on the toner cartridge itself. If they appear dirty or tarnished, gently clean them with a dry cotton swab.

   Never use water or oil-based cleaners on electrical contacts. A dry cotton swab or a swab lightly dampened with isopropyl alcohol works best.

4. If you are using a third-party or refilled toner cartridge, try installing a genuine HP cartridge. Some HP printers reject non-HP cartridges or cartridges that have been refilled.

   HP printers use a chip on the cartridge to identify it. Third-party cartridges sometimes have chips that are not recognized, resulting in error 31.

5. If a genuine HP cartridge in good condition still causes error 31, the toner sensor inside the printer has likely failed. A technician can inspect and replace the sensor.

   Toner sensors are relatively inexpensive to replace. If the printer is older and sensor replacement costs more than the printer is worth, replacement may make more sense.