How to Resolve OKI Printer Error Code 990?

Oct 06, 2026 2 min read 155 views

What Is OKI Printer Error Code 990?

OKI Error Code 990 is a waste toner sensor recognition error. The waste toner container inside your OKI printer is a vessel where extra ink is collected during the printing process. When the machine is unable to detect either the drum unit or the toner cartridge, this sensor recognition error occurs. As a result, the printer cannot determine how much ink is still present in the units.

The waste toner container also needs to be replaced every time the toner cartridge is changed. If it is not replaced or is not seated properly, the error 990 will appear on the display.

What Causes OKI Error 990?

The waste toner detection sensor is designed to track the extra ink levels in your OKI printer. When the printing machine fails to detect the drum unit or cartridge properly, the printer cannot read the ink levels, which triggers the Error 990. Common causes include:

Dirty or dusty waste toner sensor
Toner lever not pushed all the way back
Drum unit not seated properly
Waste toner container is full or improperly installed
Sensor arm stuck or blocked by toner residue

Step-by-Step Solution for OKI Error Code 990

When your OKI Printer displays the error code 990, follow these steps carefully:

Step 1: As soon as the error code appears, examine whether every single blue toner lever is pushed towards the back position
Step 2: Open the printer and inspect the waste toner sensor
Step 3: Find the sensor - it is generally located at the back of the plastic cover on the side of the drum unit
Step 4: Remove the plastic cover and clean the silver sensor arm using a small lint-free cloth. The toner residue on the sensor is an extremely fine powder and is easy to remove
Step 5: Make sure the sensor lever on TS1 is pushed upwards into its correct position
Step 6: Clean the sensor arm thoroughly, removing any dirt, marks, or toner stains
Step 7: Push the sensor lever firmly in the upward direction - if you do not move it upwards, the machine will not be able to read the sensor on the drum
Step 8: Push the disc upward into its locked position
Step 9: Close the printer, power it off, wait 30 seconds, and power it back on to check if the error is resolved

Additional Tips to Prevent OKI Error 990

Always replace the waste toner container when you change the toner cartridge
Clean the sensor area every time you replace consumables
Handle drum units carefully to avoid getting toner dust on the sensor
Make sure all components click firmly into place when reinstalling them

OKI Printer Error 990 FAQ

Q1. Does OKI Error 990 mean I need to buy a new drum unit? Ans: Not necessarily. Error 990 is usually caused by a dirty sensor, not a failed drum unit. Clean the waste toner sensor and the silver arm first. In most cases, this resolves the error without needing any new parts. Only replace the drum unit if cleaning the sensor does not fix the problem and you have confirmed the drum is at the end of its life.

Q2. Can I reset the OKI Error 990 without cleaning the sensor? Ans: You can try power cycling the printer by turning it off, unplugging it for 60 seconds, and plugging it back in. Sometimes this clears the error temporarily. However, if the sensor is actually dirty, the error will come back. Cleaning the sensor only takes a few minutes and is the proper fix to prevent the error from recurring.

Q3. Which OKI printer models commonly get the Error 990? Ans: Error 990 is commonly reported on the OKI C5300, C301dn, MC363, B4300, C330dn, C530dn, and C610 series. Any OKI printer with a waste toner detection sensor can potentially show this error if the sensor gets dirty or the toner lever is not fully engaged.