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330i "Check Engine" light

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BMW 330i 2003.
“Check Engine” light has been on for months.
No performance problems noticeable in the car.
But no one can seem to figure out what’s wrong.
Can this be a computer issue?
I would appreciate any suggestions.

No one can provide even a wild guess without more info.
You state no one can figure out what’s wrong but does this mean that the car has been at least scanned for codes repeatedly with nothing being found or what?
How many times has it been to the shop and what kind of shops has it been to?

That is odd. A persistent CEL is generally something that makes the engine run open-loop, but if it were running open loop, the fuel economy would be rotten.

If you have not done so already, take it by a car parts place that will read the computer codes for free, and post the codes that they find.

On a 2003, you probably have well over 100k miles on this car, right? Your oxygen sensors are supposed to be replaced at 120k miles. Not cheap.

I have a 330ci with 80k on the clock. I get a CEL every once in a while due to an EVAP Purge Control Vavle failure. This is a very common issue on these engines, and not very expensive to fix. I have a code reader so I just clear it every once in a while and it has no effect on performance but may have one on emissions I think.

Like the previous post said, most parts stores will read your codes for free. It really can be anything.