If it is an OEM, TOYOTA sensor, there is two series of numbers, something like XXXXX-XXXXX in the first series, if the last #is a 5 it is a o2 sensor, if the last # is a 7 it is a air fuel sensor so XXXX5-XXXXX =o2 XXXX7-XXXXX = a/f sensor hope this helps. Login to read more.