DIY on removing oxygen sensors out of my 1996 BMW 328I. This is a fairly easy job, and certainly worth it as the dealership originally quoted me more than $600 to replace two of them! 

The two that I replace in this video are pre-cat, and are the ones that should be replaced AS SOON AS POSSIBLE. This is because the two sensors that are pre-cat can cause damage to the catalytic converter when they go bad. 

Two sensors cost $200, but a new cat can be upwards of $2,000!  

I recommend replacing them one at a time so that you an keep track of where each one run's to on top of the motor.