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?
check engine light
Jun 07, 2007
6 Replies
"RM" wrote
Usually O2 sensor.
FloydR
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.
Which means something associated with the emissions control is off. It can be a coil (you'd notice a rough runner), O2 sensor, loose gas cap or a host of other sensors not quite in spec. Dump the code to find out what needs what. OBTW, Check Engine usually doesn't effect drivability though some things (upstream O2 sensor) can effect mileage.
R / John
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.
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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