No worries James,

If the problem is very occasional, you should try to clean the sensor with a MAFS spray cleaner(I think that is what Jess and Dan need....ha ha!). Also, make sure your air filter is very clean. Then, re-test using your code reader from time to time.

Finally, these X5(e53) cars aren't worth much these days....around $6k-$10k. My Chinese sensor had worked well for years, until I traded-in the car. So be careful not to over-capitalise on the maintenance.