323CI 2000 camshaft sensor A

hello, guys i am new here an d the proud owner of a 323CI 2000 beautiful driving machine, i own this car for the past 2 years and here is my first problem, the service engine ligth is on now and i i took the car with a friend of mine ( mechanic) not a BMW specialist but he was able to hook his computer or diagnostic OBDII in to the car port and was able to reset the service light and acouple of days later came on again this time he check what it was and the camshaft positioning sensor "A" was the result on his diagnostic, reset it again and a few days later it happend again and same thing came with the same results, now there is two pulse generator sensora on this car does anybody knows with is the A and B one is at the front of the engine on the left hand side standing at the front of the car and there is another one at the right side of engine next to the head, i will apreciate any help here sinse i donnt whant to spend the money on two sensors,

regards,

MEX323CI