Heated Oxygen sensor Malfunction

ok, I am getting a heated oxygen sensor malfunction (bank 1 sensor 1) and (bank2 sensor 1). From the codes via the autozone scanner. The code's are P0135 and P0155. The check engine light came on and it said the heated oxygen sensor malfunction (bank 1 sensor 1) so I replaced the sensor, then I had the codes reset. The next day the the check engine light came on again saying the other sensor is bad so I replaced that (bank 2 sensor 1). I had the codes reset again, then the next day the light came on again saying the same thing but for both sensors. So I figured the sensors are not bad but something else is causing this problem. Anyone have any ideas? Its driving me nuts.

1998 Ford Taurus 3.0 DOHC

Check to see if you are getting 12V to the heater side of the sensors.Also,giving make,model and engine may be helpful.

What would cause 12v to not get to the sensor? I checked the battery, and thats reading 12 volt and about 13 or 13.5 when running.

Fuses,wiring,relays,etc. But you need to check at the sensors themselves to see if this thought is valid. If you have power and ground then this is not causing your problem.

It appears that voltage is making it to the sensors. Which I think is good. The car has 98000 miles to..

Been working overtime-did you check the ground wire ( at the sensor)?