There are 4 O2 sensors, a set of GOOD ones will likely cost $300-$400. I have bought a complete set at Amazon.ca for a lot less, but those are of so-so quality. I do all my own work on items like that, so if they go bad it is only a bit of my time. If you are paying a mechanic, you might want to use the Bosch brand sensors. Also check to make sure your cats are not plugged up. They are VERY expensive to replace. Or you could just replace them with pipes (cat delete). This would trigger your check engine light permanently though.


I don't know about your mechanic, but if he is not really familiar with BMWs you will be paying a lot for his tuition.



If he is knowledgeable about BMW's, he should already have the proper test gear to confirm the sensors.



With an X5 of this age, if you cannot do a lot of the small jobs yourself, its going to become a very expensive car very quickly. Might be time to trade up.


I know this isn't truly helpful, but the the truth is that an X5 is not for someone on a tight budget.


Good luck
K