When i boughtmy cady the service light was on and the guy said it may be from when the engine was put in. So i had got the scan tool out and got these codes

P0151 - O2 SENSOR LOW VOLTAGE BANK 2 SENSOR 1
P0154 - O2 SENSOR NO ACTIVITY BANK 2 SENSOR 1
P0174 - O2 SENSORTOO LEAN BANK 2 SENSOR 1

2 days ago i reset the codes and took it for a drive and got 2 blocks and the light came on. so today i checked it again and got the same codes.

I checked the connection from the sensor to the conector and everything seemed ok (no broken wires)but im not sure where else the wires run after that. has any body had this happen or do i really need to buy the o2 sensor? I haven't noticed any problems but as far as the code saying im too lean im sure im going through gas more that i should.

 

That's the same set of DTCs I got when one of my O2 sensors failed. Does your scan tool allow you to see a graph of O2 sensor operation?

If so, get the car fully warmed and monitor Bank 2, Sensor 1. It should be roughly a sine wave swinging quite regularly between 0.3V - 0.6V. Failed or failing sensors will often spend a lot of time flat linedwith humps instead of waves.

If it looks good at idle (I'd suggest comparing to the graph of Bank 1, Sensor 1), then take engine up to 1000-2000 RPMs for about two minutes and then return to idle. The output should very rapidly swing outside the 0.3V - 0.6V range and stay outside that range for more time than it takes for an in-range cycle. If not, replace the sensor.

If things still look OK see if your scan tool will report loop status for the sensor. With the engine fully warmed and operating at 1000-2000 RPM it should be operating in closed loop. If not, the sensor is bad. Ifyou still find no problem check the wiring to the PCM (theengine "brain") located underneath the air cleaner. The O2 sensor connects in connector #2 (clear) atterminals 69 and 70 (purple/white and tan/white wires).Check for bad wire or connections. Likely you'll find the problem in the very first step when you observe the waveform at idle, especially compared to the other pre-catalytic sensor (Bank 1, Sensor 1).

At least the front sensor is easy to replace. The rear sensor (the one that failed in mine) is a bear. Make sure that the engine is warm when you remove the sensor and treat the replacement with care. They're robust, but easy to damage by contamination.