A Audi mileage of 2000 km mileage 120 thousand A4. After the repair of the other cars, the car can't start failure, and the instrument panel's anti-theft indicator lights up. After receiving the car: using the diagnostic instrument to self diagnose the engine system, there is a fault code 17978, meaning that the engine control module is blocked. This indicates that the engine is prohibited from starting from the anti-theft system. Check the ignition key, the surface has no trace of damage, but because it is a second-hand car, only this ignition key, can not change the key test. Login security system (address code 25), the result is unable to communicate. Log into the dashboard (address code 17), enter the diagnosis menu smoothly, but only read the 14 bit identification code of the anti-theft system, read no 17 vehicle identification codes and read the fault code 01177, meaning that the engine control module is unauthorized. In order to disable the starting state of the engine system, the following operation is done: enter the anti-theft system (address code 17), select the "match function (10)", enter "00", confirm, clear the adaptive value. At this point, the anti theft indicator lights go out, indicating that the match is successful. Try starting the vehicle, the engine works smoothly, and the trouble is completely eliminated. The car is equipped with the immobilizer- II anti-theft system, and the anti-theft module is integrated into the dashboard. Therefore, the diagnostic menu of the dashboard must be entered when testing. This case occurs when this kind of fault occurs. It may be caused by insufficient system voltage or repeated starting. Generally, it does not need to change parts. It can open the ignition switch for a long time or use the diagnostic instrument to eliminate the adaptive value.