take out the battery. Or if all else fails take it to the garage where they will connect it to their computer and do the diagnostics
Check out the realted link for some advice on how to reset the computer in your 2003 BMW 325I computer.
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Reset inspection light on 1989 bmw 325i
You need a scan tool to plug into OBD port
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reset service engine light on BMW 325
The brake warning light on a 2005 BMW 325i can be reset by connecting an OBD II code reader. It can view and clear error codes detected by the computer.
idle control valve
Depending on the year there may be anywhere from 1 to 8 computers in a 325i
this is a German car, there is no "reset" button,
To reset the security system on a 1995 BMW 325i, first ensure that the car is in the "Off" position. Insert the key into the ignition and turn it to the "On" position without starting the engine. Leave it in this position for about 10-15 minutes to allow the system to reset. If the problem persists, consult the owner's manual or a professional mechanic for further assistance.
65L i believe