Malfunction: a 2005 year old Shanghai Volkswagen Polo 1.4 L sedan (manual transmission) "suddenly stopped walking in a long distance." Inspection and analysis: the vehicle speed sensor is installed at the end of the half shaft of the transmission, and the meter drives the speedometer according to the speed sensor signal. In order to judge whether the instrument receives the speed signal, the fault detection instrument is used to diagnose the instrument system, no fault code, the road test read the data flow, and observe the indication of the instrument. The speed meter does not respond. Then the speed signal in the engine control unit is read, the function 01-08 is selected, the speed signal is normal, the speed meter is suspected to be damaged, the instrument is replaced and the road test is carried out after the code and the anti-theft match, the failure is still. After consulting the binding data, we know that the configuration of the Polo car network control system can transmit data through the network and realize data sharing. That is to say, the signal data of a sensor can be transmitted from the network bus to a plurality of control units. When the speed sensor is damaged, the instrument can not receive the transmitted sensor signal, and the speedometer stops working. The engine control unit reads the speed signal of the ABS control unit by summing up the speed signal, so that the speed signal can be read in the data stream of the ECU. The ABS is equipped with 4 ABS wheel speed sensors. The ABS control unit calculates the speed signal according to the ABS wheel speed sensor, and then transacts it through the network president. Check the speed sensor, pull off the conductor side connector, and measure the wiring connection, normal. Check the speed sensor and find that it is damaged. Elimination method: change the speed sensor.