Why is my ABS Warning Light ON? There are lots of reasons why the airbag warning symbol light is illuminated on your dashboard, and there is no straight answer. However you do have the power to diagnose the fault and fix it yourself. You don't need to take it to the garage or dealer. You can read the diagnostic fault code or trouble code with your own diagnostic scan tool. The ABS system is also linked into the ESP BAS ASR EPB systems.