BMW E46 DSC and ASC light on
What causes the E46 DSC or ASC light to come on?
Common causes are the brake master cylinder pressure sensor, the steering wheel position sensor, a wheel sensor wiring fault and a faulty brake light switch. Read the fault codes first, because the symptom can look the same with different faults.
What do pressure sensor codes 5E20 and 5E21 mean?
The master cylinder has two brake pressure sensors: 5E20 is sensor 1 and 5E21 is sensor 2. Replacing the faulty sensor turned the lights off. You can identify the faulty one by unplugging the connector of the other sensor and comparing the live data readings.
What should you check before replacing an expensive part?
Check the brake fluid level and the brake hose connections, because low fluid has caused a steering angle sensor error. A weak battery can also trigger the lights, so charge the battery and reset the fault codes. Moisture in the sensors can turn the lights on temporarily.