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Old 11-08-2012, 09:47 AM
Supercourse Supercourse is offline
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Location: British Columbia, Canada
Join Date: Feb 2008
Posts: 3,891
Mein Auto: 2004 X3 2.5i
Originally Posted by BigglesTAP View Post
Strangely immediately after the reset the bulb fail light came on and I can't see one that is out.

Most likely one of the rear tail and/or brake light bulb pairs.
Difficult to diagnose by quick look while parked as when one bulb dies the other one takes over that function.
Although you will see both sides light up when the brake pedal is depressed, there will be a difference if you look carefully.
This has fooled quite a few owners on this forum.
Best to replace at least 2 bulbs anyway while you are at it - they get dimmer with age.

Is it possible it was a one off trigger? Yes. Could have been moisture in the connection to the O2 sensor, or just a random voltage drop or spike as the battery had got a bit discharged while unused for a week.

How many O2 sensors are there on the X3? 4 - 2 pre-cat and 2 post-cat.
Is there a way to test the O2 Sensors in situ? Don't know, but unlikely to be the pre-cat ones as that would most likely affect air/fuel mixture and give bad idle.
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