When you read codes, they sometimes come up with faults relating to O2 sensors. This may well point to 1 of 4 sensors on a 6cyl/8cyl car, so here is a diagram to explain the terms a little better.
- Bank1 Sensor 1 and Bank2 Sensor 1 are the pre-cat sensors;
- Bank1 Sensor 2 and Bank2 Sensor 2 are the post-cat or after cat sensors.
-Addition by Ronnie-
To add to this, if you do get a o2 sensor/lambda sensor fault code come up, you should first check for any unmetered air that may be entering the engine from split induction pipes, vacuum pipes or breather pipes, all air should travel past the air flow meter otherwise it will give you a running fault and can trigger a o2 sensor or MAF/MAP sensor fault code.
o2 sensor HEATER fault codes though are more likely to be down to a failed o2 sensor, but a check of the wiring should be done first as well as a check for voltage on the heater wire.