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A 11 4600KM Volkswagen Golf Car with a mileage of about 1.4TSI. The owner reflected that the vehicle did not affect the driving performance of the vehicle. After taking the car: using VAS5052B detection, the engine control unit is stored in the fault code 01674, meaning ECM/PCM power relay abnormal, the fault nature is accidental; fault code 08487, meaning that the acceleration pedal position sensor switch E circuit voltage input is low, the fault nature is accidental; fault code 08482, meaning acceleration pedal The position sensor switch D circuit has low voltage input. Read 01-08-062 group data flow, the third area (acceleration pedal position sensor G79 feedback signal) data shows 0, indicating that G79 has no signal output / reception. Turn on the ignition switch and accelerate the pedal to the end. G79 still has no signal output / reception. Refer to the circuit diagram of the accelerator pedal position sensor, the terminal T94/78 of the engine control unit J623 is checked with the multimeter to 4.24V, the standard value should be 0; the J623 terminal T94/78 to the body resistance is 786 Omega, the standard value should be about 10 omega; the J623 terminal T94/55 and the body resistance to 10.1 omega; J623 terminal T94/15 to the body. The resistance is 5.5 omega; the terminal T94/16 of the J623 is 55 Omega to the body resistance; the terminal T94/81 of J623 and the terminal T94/82 voltage (the power supply voltage for the 5V sensor); the J623 terminal T94/15, the static feedback voltage varies from 1.3 to 1.6V in the process of stepping down the accelerator pedal. According to the measurement results, it is judged that the internal pressure of J623 terminal T94/78 is too large. After replacing the engine control unit, the data stream of the engine 01-08-062 group is read: one area displays 16%, two areas display 82%, three display 14%, four display 7%, all in the normal range. After on-line matching, the engine can start normally and the road test conditions are normal. After testing, all the control units of the gateway are detected and no fault codes are generated. After determining no abnormal situation, begin to install the front guard plate of the reflow tank, just at this time, the EPC lamp on the dashboard appears to alarm again, and the fault code 08482 appears again. After reading the data stream of the engine group 01-08-062, the third zone value also shows 0. Turn on the ignition switch, the voltage of T94/78 is 4.51V, disconnect the control unit connector, and the voltage goes away, indicating that the voltage can be closed through G79. The terminal T6h/2 of G79 still has the power supply voltage of 5V. From this analysis, the terminal T6h/3 of G79 also shares a large partial voltage resistance. The terminal T94/78 of the measured J623 also produces a 150k ohm resistance to the body, which indicates that the newly replaced engine control unit has an internal grounding fault. The newly replaced electric control unit is again damaged in the same - position internal circuit, obviously indicating that the fault is the short circuit of the G79 terminal T6h/3 in the online beam and the external power supply, and this short connection or accidental. The voltage disappeared after disconnecting the conductor side connector of the engine control unit, indicating that the short supply should be controlled by the engine control unit. Tracing the environment of the fault, the fault is generated when the water trough guard plate is installed before the fault is restored, thereby judging the fault point on the engine wiring harness. After careful examination, it is found that the engine harness should have two positioning points in the flow channel to fix the wire harness, but the clamp of the 1 fixed points on the right side in the flow trough is not stuck, which causes the extrusion phenomenon of the engine harness and the wiper bracket. The external insulation protection layer of the wire harness at the extrusion is stripped and the gray / red line connected with the terminal T6h/3 of the G79 and the 1 red / green power lines are both worn out. The two damaged lines are not likely to have a direct short circuit. However, the two lines can contact the wiper bracket at the same time. When contact, the 12V voltage can be brought to the terminal T6h/3 of the G79, although the time of the short-circuit is short, it is sufficient to damage the engine control unit. Since the terminal T6h/3 of G79 has increased the resistance of the body, it will still share the most of the voltage of the terminal T6h/2, causing the terminal T6h/4 to be only sensitive to the weak voltage, and the data flow of the 6 sets of third zones is shown to be 0. When the engine control unit monitors the abnormal signal voltage of G79, the fault code 08482 is recorded. Because the signal from the G185 and the feedback signal of the electronic throttle are normal, the electric control function of the engine is still effective, the vehicle can run normally, but the EPC lamp is kept in the alarm state. Repair the damaged area of the wiring harness and re fix the wiring harness according to the requirements so as to ensure that the wiper bracket and the wire harness do not interfere with each other. Once the confirmation is correct, replace the engine control unit again. After matching the new control unit, the engine starts smoothly, the fault lamp is no longer lighted, and the trouble is completely eliminated.