Oxygen Sensor

[sswenson]

1996 Grand Caravan SE 3.3L The check engine soon light is on and I am getting o2 sensor code 21. I have disconected the batt twice to clear codes to be sure and after some time i keep getting same code back.
Have any of you had this and which one seems to go out first the one before converter or the one after converter. I don't really want to replace both at one time but without getting exact code to which one it is it will be only a guess to which one is going out.

[QWESTER]

too lean gives 51
too rich gives 52
neither rich nor lean condition gives 21 which is ambiguous. does it mean sensor should be replaced? i believe so but i'm not sure. manual is confusing here.
using silicone sealants can destroy oxygen sensor.

[otto man]

I believe you can get them for less than $50 with the factory plug ends so the worst it is going to be is $100 plus a couple of hours of time. Not bad to solve the problem in my opinion. I have paid over $100 for a generic (no plug end, slice and splice) for other cars.

[lakeman]

If your driving a 96' with origional O2 sensors you might as well change both of them now 'cause they are long over due. I have two 96's and I have had to replace four sensors.