5-Series (E12,E28, E34, E39, E60)Chat relating to the BMW 5-Series of all generations. Specific models include: BMW 518, BMW 520, BMW 520i, BMW 530i, BMW 528i, BMW 530i, BMW 518i, BMW 524d, BMW 525i, BMW 525e, BMW 528e, BMW 540i, BMW 535i, BMW 520d, BMW 525td, BMW 525d, BMW 530d, BMW 525i/xi, BMW 530i/xi. (BMW 5-Series Forum)
Hey. Often times the check engine light will come on due to the gas cap not on properly. I would take the cap off, slowly put it back on tightly, then restart the car three times. The third time the light will go out if it was the cap. If not, take it to AutoZone and have them hook it up to the computer (for free) and have them tell you what code is showing up. It could be a bad sensor, a bad plug, or anything.
How many miles do you have on your car?
It might not be the O2sensors....they always tell you it is, and it ends up being not!
If you do not have like 80k and up, it's probably not the O2sensors.
And I bet it is not the gas cap either.
Cosmos is right.....For O2 sensors think "fine tuning" example? too lean vs. too rich mixture. O2 sensors will TRY to correct but when too much to deal with; O2 sensor becomes overwhelmed. This will trigger another code of "O2 sensors CONTROL LIMIT" again overwhelmed control limit makes one think bad O2 sensors especially the pre cat ones (2 in number) where in fact they are innocent and working so hard to compensate for example to the huge leak somewhere around the intake ...gaskets, vacuum hoses etc etc. a good way to check for those vacuum leaks is to spray break cleaner around the suspected area of leaks or the intake manifold, hoses ; if in fact there is a vacuum leak the intake will suck the break cleaner fluid and the idle will change .Note: for huge leaks you may well hear hissing noise also..etc etc. Once you rule out the leak then we will go for the next step.
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