the ecu will know what the leds should read so with some out it tells you.if you fit a new unit the ecu will get the correct reading and cancel warning.when you plug the bmws into code reader its tells you faults and you can check circuits and even the parking sensers it knows which one is faulty.when you have replaced the faulty part sometimes you need to cancel code to put warning off.this is why it is cheaper to use the right part or some one like europarts as they are compatable
bob
May 2012
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