When and what to change for my BMW e46 Brakes?

I have a 2001 BMW e46 316i



I noticed that when I am climbing a hill or coming down a hill at speeds, my brakes sometimes makes a squeky noise, sometime ago a mechanic said to me that my brakes needs changing, as the brake oil had come down quite a bit.



Now I am going to buy the brakes today from BMW, I am thinking how many should I buy, I am thinking of buying all 4 brakes, but I might be wrong here. It is worth buying just front 2 or all 4.



Also, on a more seperate note, when I was driving this morning, on a wet icy road, coming down the hill, the car skidded and i temporarily lost control, it was going sideways to hit another vehicle, I am note sure if this is related to the brakes or just the road condition, I did put on the ASC function afterwards, is this the right thing to do and what else do I need to check in the car ?When and what to change for my BMW e46 Brakes?Firstly, your ASC is turned ON by default. (No light = ON, orange ASC light on = OFF).



Brake pads should be changed in pairs. Also, you will need to buy a brake wear sensor.



You'll need 1 sensor for the front, 1 for the rear.



If the mechanic said you have brake fluid leaking, you have a more serious brake problem that may require the brake calipers to be changed too.



Depending on how worn your rotors are, you may also need new brake rotors (discs).



You can tell by looking through your wheels how much brake pad life you have by looking at the thickness of the brake pad friction material. Then judge by yourself whether you need 1 or 2 pairs. Squeeky noise does not necessarily mean you need new brakes.



Edit: it's advisable to change your brake sensors everytime you change your pads even if the sensors have not physically rubbed on your rotors. It's not expensive, in the US, it's $10 a piece. The reason is the plastic piece that clips onto your rotor normally would become brittle with age and heat from your pads. It's easy to break it when you remove it.