A Volkswagen Polaris with a mileage of about 50 thousand km, equipped with 1. 8L electronic controlled engine and automatic transmission. The malfunction of the vehicle is as follows: after the engine starts 1s, the engine will automatically extinguish and the anti-theft warning lamp will light up. According to the fault symptoms, the anti-theft function is activated, resulting in the interruption of fuel injection function. The engine system and anti-theft system should be checked. Connect the diagnostics, select address code 01, query engine, have a fault code, the content is "17978, engine control module locking". Perform fault code clearance function, trial run, fault still, indicating fault exists. Choose address code 17, check the anti-theft system, there is a fault code, the content is "01176, ignition key signal is too weak." It is legal for the driver to know that the ignition key is currently used, which has always been able to operate normally. The cause of the analysis may be the damage of the ignition key. Using the ignition keys of two other original vehicles, the engine starts smoothly and the burglar warning lights are normally extinguished. Replace the damaged ignition key, re engage the anti-theft match, and eliminate the trouble thoroughly. Bora ignition key has a chip inside, the chip stores anti-theft code. If the chip is damaged or the performance is bad, the anti-theft control module can not read the anti-theft code, and the anti-theft warning lamp is lighted. The engine control module interrupts the fuel injection function after receiving the anti-theft lock signal through the data line, and the vehicle can not start.