A Mercedes E320 car with a mileage of about 100 thousand km, a M112 engine and an automatic transmission, and a chassis model of W210. User response: the vehicle can not turn on the ignition switch with the ignition key, and the vehicle cannot start. After receiving the car, it is found that the ignition key can not be transferred to the Key on gear, and the steering column is also locked. The fault may be related to the driving authorization function. The self diagnosis of the connection diagnostic device failed because the 15 power was not connected. Remove the ignition switch assembly, check the electronic ignition module power line, normal. From the driving principle, it is known that the coded data of the ignition key is transmitted through the infrared mode. If the electronic ignition switch module has good performance, the failure should be the failure of the ignition key. There is also a cause of failure (rare) is the damage to the steering column lock control module (N26/5), which is because the module is a component of the driving authorization system, and the electronic ignition switch control module needs to receive the unlocked signal of the steering column to release the lock spring inside the ignition switch, '. As the function of the convenient mode is also activated by infrared signals, a convenient mode can be used to determine whether the infrared emission function of the ignition key is normal. By holding down the remote key of the ignition key, there is no response to the door glass and sunroof, indicating that the convenient mode function fails, and it can be sure that the fault is in the ignition key itself. Open the shell of the ignition key, you can see the internal circuit board and light-emitting diode. After careful examination, it was found that there was a slight crack on the circuit board. Welding, igniting the ignition key, starting the vehicle and running the engine smoothly. Press the remote key of the ignition key and activate the convenient mode function to show that the trouble is completely eliminated. The DSA3 ignition key has many functions. Knowing these functions helps to find out the cause of the failure.