The Service Engine Light on your BMW 3 Series is monitored and controlled by the Engine Control Module or ECM. It keeps track of all routine maintenance and servicing requirements of your BMW. When this light illuminates, you should have your BMW serviced before attempting to manually reset the light. The best way to reset it is to use a computerised scan tool obtained from your local auto parts retailer. This tool can be purchased or borrowed for free from most auto parts stores.
Put the key into the ignition and turn the vehicle to the "on" position but don't start the engine.
Find the diagnostic port under the driver's side dashboard near the pedals. Plug the computerised scan tool into this port. The battery from the vehicle will automatically power on the tool.
Find arrows on the faceplate of the scan tool and use them to scroll through the menu until you find the "Read All Codes" command. Select this command.
Scroll through the menu again and find "Clear All Codes." Select this option then wait for the service engine light to shut off.
Turn off the vehicle and wait five minutes. Start the engine and verify that the check engine light is still off.