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Lexmark T640

Lexmark T640

929 or 929.xx service toner sensor error

Issue description

The 929 and 929.xx service toner sensor messages indicate that the printer is having a problem reading the toner cartridge. The problem could be with the toner cartridge or with the toner sensor on the printer. This is especially true if it is a brand-new cartridge and the error started after you installed it.


  • Try installing another new toner cartridge. If you do not have a new cartridge in stock, an old cartridge or another cartridge from a working printer of the same model also suffice for this test.
    1. Power off the printer and install the second toner cartridge.

    2. Power on the printer with the second cartridge installed.

    3. If doing this clears the 929 Toner Sensor error, try printing again.

    4. If the error does not return, the original toner cartridge is likely the cause of the error.


      This is especially true if this error message started just after you installed it.

  • If you do not have another toner cartridge to test with, take this cartridge out of the printer and locate the encoder wheel on the right-hand side of the cartridge. The encoder wheel is a thin, black, plastic wheel with small rectangular notches cut into it. It is usually found just above a bar code sticker on the right-hand side of the cartridge.
    1. Try moving the encoder wheel forwards and backwards a couple of times to make sure that this wheel is not stuck.

      Note:  The encoder wheel moves only a little bit each way. DO NOT force the wheel to turn. The wheel must not be able to make a complete revolution. If it does, it is broken.

    2. If this wheel spins freely or does not move at all, you receive a 929 Toner Sensor error on the printer when you try to use this cartridge. In this case, the cartridge must be replaced.

  • If you receive this error on more than one toner cartridge, you must make sure that the toner sensor cable is still plugged into the toner sensor. Do the following:
    1. Turn off the printer and remove the toner cartridge.

    2. Look inside the printer in the area below where the cartridge goes. The toner sensor is on the right-hand side. On the back of the toner sensor assembly, you must be able to see a white cable connector.

    3. Make sure that this white cable connector is fully installed into the toner sensor assembly by carefully pushing the connector toward the front of the printer.

    4. Reinstall the toner cartridge.

    5. Close the front lid and power the printer back on.

  • If you narrow down the problem to the toner cartridge, take the following action:
    1. Contact the point of purchase and explain the situation to them. They may have a replacement policy in place.

    2. If the point of purchase cannot help you, call our Customer Support Center and we will see what we can do to replace the cartridge that is causing the error.


      • Technical Support will not be able to reimburse the price of the cartridge, but can offer you an exchange on the defective cartridge. In this case, we may ask you to send in your defective cartridge first. If you do contact Lexmark Technical Support for a defective cartridge, have the cartridge with you as Technical Support needs some numbers off the cartridge to replace it.
      • Note that we cannot offer an exchange on a refilled or refurbished cartridge. For those, you must go through the point of purchase. Click here to order toner cartridges and other supplies for your printer.
  • If you have gone through all the checks and the printer continues to post the 929 error, service is needed to isolate the problem and replace the failing component. Contact Lexmark Technical Support or a local service provider.


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