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The mileage is about 70 thousand km, the 2008 Audi TT car equipped with BWA engine and 02E transmission. User response: the car bumped for a while, then the tire pressure alarm light was always on. Fault diagnosis: the car uses a tire pressure monitoring system (TPMS) to measure the tire pressure indirectly. There is no tire pressure sensor in the tire. The circumference of the tire that is under pressure will be smaller and the number of rotating rings is different from that of the other tires. The TPMS control unit (J793) receives the speed signals from the 4 wheel speed sensors transmitted by the ESP control unit (J104) through the comfort system bus, and analyses whether the tire pressure is insufficient. After the car was tested, it was found that the tire pressure alarm light was always on. It is normal to check the tire pressure of each wheel; to reset the TPMS (i.e., to initialize the TPMS, TPMS to learn the tire pressure of each wheel, and to use the learning value as the standard value of the monitoring), the reset can not be completed. It is doubted that the TPMS or ESP system has a failure. Using VAS5054A test, enter 4C a tire pressure monitoring system control unit, store the fault code 01317, meaning the combination instrument control unit (J285), please read the fault code (static), enter the 17 unit of instrument control unit, store the fault code 00779, meaning the external temperature sensor (G17) circuit breaker or the right The power supply is short (static). According to the fault code prompt, check the line between the external temperature sensor and the control unit of the combination instrument. It is found that the external temperature sensor wire connector has the trace of maintenance, strip the tape of the wiring harness, and find that the wire inside is seriously oxidized and corroded, and the external temperature sensor reaches the letter of the combined instrument control unit. The number line is broken. Troubleshooting: repair the external temperature sensor line and remove the fault code after the test, the tire pressure alarm lights out, long time road test has not been lighted, troubleshooting.