check engine light

99 M3 check engine light is coming on regularly. When the car was new occasionally vapor lock would cause this... but one readjusted the cap and
a tank of gas later the light went off. Now it comes on I readjust the cap add gas and it goes off then a day later it comes back on.. Gas cap? sludge in the tank? sensor wearing out?
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Usually O2 sensor.
FloydR
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There are literally hundreds of reasons for the Check light to come on. You have to pull codes to find out why the light is coming on now.
The scan tool is not majic, your car is OBD II compliant, this means that pulling codes is done with a standardized tool that fits all cars. the data port is located along the bottom edge of the dash board in the general vicinity of your left leg while you are driving.

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this is the check engine light not the check light. They are two distinct different items

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The light that comes on when the gas cap is not secured is the Check Engine Light, or Check light for short.
You need to pull codes to see why the light is on.

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Find out what it is.
If it does go out when you open and close the gas cap, then get a new one or unclog the labyrinth.
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