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In my E46 BMW, the yellow check engine light always turns on when visiting Lake Tahoe (altitude ranging from 6000-8000 feet). It usually turns off if I've been there for a couple days. After many thorough performance 'test' drives, I don't hear or feel any obvious problems. I can't find anything about this when searching Google.

Is this something to be concerned about?

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I would not consider this an issue. What is happening is, as you've probably already figured out, is that your car is adjusting itself to the higher altitude. When the light comes on, it is telling you it is basically out of calibration (probably due to running too rich at the higher altitude). Once the computer can get caught up and adjusts the fuel map correctly, it gets back to running within spec and the light goes out. You can verify this by getting the codes pulled from the ECU. These are usually stored in there until they are reset even though the CEL is no longer indicating a problem.

  • But most cars seem to be able to make this adjustment without ever turning on the CEL. So either the E46 is weird in some way, or maybe it's taking longer to adjust than it should? – Nate Eldredge Feb 24 '15 at 1:13
  • @NateEldredge ... Going from a lower altitude of say 2-3000' up to 6-8000' is a huge difference. Not drawing near the air as you do down low. As long as the CEL goes out I don't think there is too much to worry about. He should get the codes check, though. Wouldn't hurt to know for sure if anything is lingering. – Pᴀᴜʟsᴛᴇʀ2 Feb 24 '15 at 1:25
  • If the OP is going to Lake Tahoe, odds are good they are coming from sea level. But I've done that exact drive, and other trips with an even greater elevation change, in several different vehicles, and never seen the CEL light come on. I agree it doesn't sound like a serious problem, but I'm not sure it's normal. – Nate Eldredge Feb 24 '15 at 1:28
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    You are right on all counts. I think the difference may his version of a "test" drive. Depending on how hard he's pushing it, may have something to do with it. It may all come down to it being a Beemer as well. I'm not sure how the computer does its adjustments. It does seem like a long time for self-adjustment, but considering he's not really feeling any difference seat-of-the-pants, I think it's not a big deal. – Pᴀᴜʟsᴛᴇʀ2 Feb 24 '15 at 1:32

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