Hello,
I have a 2001 BMW X5 4.4i with 80000 miles. Last May my check engine soon light came on so I used my ODB Pocket Scan to find out what the problem was. The code said Pre O2 sensor bank 1 sensor. After getting feedback from members of xoutpost.com I bought 2 new bosch Pre O2 sensors and installed. The light went off and I had no other Check Engine light appear until last week. The Check Engine light came on again so I reset to see if it would appear again and it did. This time the ODB error message was System Too Lean Bank 1. I called AUTOZone and they informed me that the error was for the O2 Sensor Upstream in Bank 1. My question is do I need to replace the Pre O2 sensors again just after a year or is there perhaps another issue. Please help I am leaving on a 500 mile round trip this friday. Thanks Comanche