A passageway with a mileage of about 90 thousand km, equipped with AWL engine in 2004, Passat controls 1.8T manual block cars. The user reflected that the car was unable to start. Inspection and analysis: the maintenance personnel detected the engine control unit and found that the diagnostic instrument could not enter. The K-line voltage on the diagnostic socket is 11.78 V, and the voltage drop after the connection is 2.3 V. The audio-visual inspection found that the car has been reformed. Remove the stereo and find that the rear line is chaotic. With the consent of the user, the original vehicle line will be completely restored. The engine starts smoothly and detects the engine control unit. Everything is normal. Troubleshooting: restore the original vehicle line, troubleshooting.