I am not sure if the 1624 has the black sensor arm mounted in the top cover, or the more common right side frame mounted optical sensor discribed here. With the top mounted style, it has always been a defective toner ctg..
Toner Sensor Errors are fairly frequent on all small Oki color printers. The toner sensor for each color looks through a small cut-out on the right side frame at a silver flag located in the toner's blue handle. Often the flags of new toner's are simply stuck, I use spring hook to gently free them. The flag is supposed to move up and down as the toner is stirred, if the sensor does not see the flag move is gives a toner sensor error. Also check to make sure that some clumbsy operator did not spill toner all over the sensor blinding it.
To check proper operation of the toner flag, I remove the toner from the Image unit and rotate the white gear on the bottom of the toner, about twice around should cause the flag to cycle at least once.
