P0138 still coming of after changing rear o2

[skuff33]

Hi,

I have a CEL P0138 which is high voltage bank 1 sensor 2. I blindly replaced the rear sensor assuming it was bad (original sensor 230k miles). But after about 45 min of driving the light came on with the same code.

Today I tested the new sensor with a multimeter and got the proper 16ohm on pins 1+2, but just got a "OL" reading on 1+4 when it was supposed to be over 10kohm. Is this the proper test as per the FSM? Is it possible my replacement was bad out of the box? (Denso)

Where else should I start to chase this down.

Thanks!

[remcafee]

high voltage, so great amounts of oxygen entering, start looking into catalytic converter effieciency, if you havent already, i would check the wiring make sure its not twisted up, but get a backpressure test done

[skuff33]

I believe this ended up being a malfunctioning a/f sensor (bank 1 sensor 1). It would send the wrong info and would foul the back post-cat sensor. So in case anybody runs into this in the future give it a try, what do you have to lose other than $100?