BMW E90/92 Brake Job Must Read

If you change your BMW brake pads and/or rotors, you must change both wear sensors at the same time. The BMW will trigger a brake wear warning if you only replace one sensor. I learned this the hard way.

I replaced my rear rotors and brake pads with Zimmerman Z-Coat and StopTech. For the brake sensor, I used a non-OEM brand named Bowa. Huge mistake. The Bowa sensors are one-third the price of OEM sensors for a reason. They have almost no shielding for the wire that plugs into the brake pads that rubs against your suspension causing breaks and fraying. I cannot recommend buying OEM brake sensors enough because the entire wire is protected. 

I'm certain that changing the rear brake sensor only tripped the warning light, but lets say I changed both sensors at one time. The light still would have triggered because the Bowa wires were frayed after a couple of drives. 

Please save yourself the headache and change all brake pads, rotors, and sensors at once and do a reset. It will save you the time of taking everything apart again.

Apparently the BMW computer measures the wear at both sensors at the same time. If one changes but the other is the same it triggers the brake warning light.