CEL question

[DeadpaN]

Ok first off this may seem stupid on the surface, but it'll make more sense in context.

Does the CEL illuminate while driving or when does it come on? You see luckily I have a code reader and I've pulled codes like "random misfire-unknown cylinder" to "secondary air injection" to "disconnected battery". So far I've been able to troubleshoot and fix all problems and no more codes.
But if I never ran the scanner, I wouldn't have known....the Cel lights up with all other instrument panel lights during start up and then goes out like all the others (abs, oil, etc.). Is this working properly or am I looking at some kinda ECM/OBDII troubleshooting?

Thanks,
Eric

[andyman7931]

My CEL with my cylinder 1 misfire problem flashes on while driving when the problem first starts, then eventually it stays on. I have the scanner so I can clear it. I found that once the light is on it'll stay on until I clear it, even if I shut the car off and restart. I'm guessing that if you disconnect the battery for a while it'll reset as well.

Are there some codes that don't trigger the light? You mentioned disconnected battery, I would make that a non-critical error while a cylinder misfire would be critical. In the software I write at work for grinding machines I have 2 levels of errors like this, just curious if BMW does too :-)

[DustenT]

There are "soft codes" and "hard codes". I'm not sure how often a problem has to occur to make it a hard code.

Soft codes are generally fluky and happen during extreme temp (for me at least).

Soft codes don't set the light, but hard codes do.

[Tyler]

Hard codes are normally major faults, only the serious ones stay on your computer.

[DeadpaN]

Hmmm, well as far as the misfire thing goes, eventually it called misfires on Cyl's 2 & 4. After a set of Magnecors no more probs. but wouldn't that be a serious enough code to trip a light? And the battery one, I think that's 6C, it comes up of course whenever I disconnect it for something...

[KetteringTi]

Yes, the CEL is supposed to illuminate upon startup, if that was one of your questions. It's an instrument cluster check.

[DeadpaN]

Yeah, if I wasn't clear with the orig. ? my point was that it appears on startup but then does not appear with stored eng. codes.