2004 BMW 325 check engine & brake pad lights

The thermostat sensor (MAP thermostat) if damaged, will indeed command the service engine soon lamp on. The brake issue will be caused by a cut sensor and unless they get replaced, the "check brake linings" warning will be displayed. As to the need for replacement of the rotors, the commonly held belief is that if the pads are worn and the rotors are beyond tolerance, then replacement is needed, if the rotors are within tolerance and do not have excessive and/or uneven wear, they may be left in service. Most independent shops might use this as an opportunity to exact profits (and the dealers too) at the customers expense. The minimum thickness of the rotor is stamped into the rotor and it is the benchmark. Ask to see the rotor, ask for the minimum thickness measurement, hold them to account. If there is any more assistance that I can provide please repost. Dr. Hagerty

thanks for the response. That most certainly answers my question to the thermostat sensor question. As far as the rotors, I know I need new rotors. But I changed both front and rear brakes and the sensor wont go off. At that time I noticed that I need new rotors. So I was wondering when I change my rotors(front ones only needed)...will that make the brake sensor go off or do I need to replace those sensors?

The sensors have a wire running through them that if cut will illuminate the light, so yes you need to replace the sensors. The rotors have nothing to do with the light being on.