O2 Sensors - OBDII P0146 & P0147

'97 Isuzu Rodeo 3.2L - 128000 miles My check engine light came on about 2 weeks ago, so I took it to AutoZone for a free OBDII test and I got the following errors:
P0146 HO2S Insufficient Activity Bank 1 Sensor 3 P0147 HO2S Heater Circuit Bank 1 Sensor 3
Now I thought that this was for the O2 sensors malfunctioning. There are three O2 sensors on my Rodeo. Starting from the engine towards the back of the vehicle, I replaced the first sensor, left the second, and replaced the third. After replacing these i disconnected the battery for at least a minute but the Check engine light keeps coming on. Any help?
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