Failure phenomenon: a 2009 annual Shanghai Volkswagen POLO AccFast 1.4 L sedan, 2 300 km mileage. 3 days after users complained that the vehicle is parked the engine can not start properly.
check analysis: the author preliminary analysis of the cause of this failure is the battery power loss. Cause battery power loss of the battery itself includes self-discharge, the vehicle does not turn off appliances or drain line, and the presence or virtual connection to ground short circuit caused. Considering the short time because the car purchase, and therefore are less likely to self-discharge battery itself. I fully charged the battery first, and then use the Shanghai Volkswagen dedicated battery tester MCR-341V detect the battery is normal, the test result is good battery condition. At this time, attempt to start the vehicle, the vehicle can start smoothly.
ruled out the possibility of battery failure, I began to check for electrical appliances on the vehicle where there is a leakage. After communication with the user that, when the vehicle is parked all the lights and other appliances are turned off. Then the vehicle should exist leakage phenomenon appliances or lines, so I set out to find the specific leak location. First, turn off the ignition switch, lighting and other electrical appliances, and disconnect all the doors closed luggage compartment lights; then clamp measurement fault diagnostic VAS5051 / B of the battery discharge current, after waiting for 10 min, all vehicles entering the control unit sleep state, the discharge current was observed as 0.26 a, the car normal discharge current in the sleep state in 0.03 a or less, the discharge current is found excessive car.
Thus, according to the author to find the position of the drain discharge check the basic method. First, remove the instrument panel of the left side cover fuses, each fuse sequentially removed, and observing whether the discharge current decreases. Current still does not change the result removed all the fuses, which can determine through these lines and fuses with electrical leakage phenomenon does not exist. Then I have not been to fuse these lines and electrical appliances were checked. First, the starter and generator disconnect plug discharge current readings and observed, no significant drop; sequentially pulled each system control unit of the vehicle and observe the discharge current reading, disconnect all plug when the vehicle network control unit J519, found current rapidly dropped to 0.02 A, and then plug in the plug current increases rapidly all, in which the initial battery discharge power is determinedFlowing a large vehicle due to leakage caused by the network control unit J519. Taking into account the probability of the car as a new car, and failure in the daily maintenance of the in-vehicle network control unit is small, the author is not jumping to conclusions.
The control unit has a vehicle network load management, lighting control vehicle, fuel pump control, windshield washer and wiper control, exterior mirrors and the heated rear window heating, a turn signal control horn and control functions. It performs a corresponding function according to different signal relay inside the control input, the signal acquired by the sensor is not a normal internal control unit will cause the operation of the relay error, resulting in leakage. But I have not found onboard network controlled by a control unit with electrical signs work.
a plurality of the on-board network control unit plugs, each plug and unplug the author observed sequentially discharge current, when disconnect the plug pin 5 T5a (black), 6-pin plug T6J (brown) and T6K (red) when any one of the discharge current rapidly dropped to 0.02 A. The circuit diagram can be seen, the T5a plug pins 3, 4 and 5 wires for connecting the wiper motor. In order to verify whether the problem is on the wiper, the author all plugs plug-board network control unit, and then pull the plug wiper motor and observing the discharging current, the discharging current at this time is about 0.26 A, thus eliminating the wiper motor failure . No. 2 conductor pin is a ground line T5a vehicle network control unit analyzes the discharge current I decreases rapidly when disconnect the plug T5a to 0.02 A, it is because the plug within a vehicle network line is a ground line of the control unit, and this line plug connected and electrical appliances and there is no problem.
to further narrow the fault, the fault point is likely to appear on line T6j 6-pin plug and connected appliances. 6 T6j only three pin plug pins have wire leads, the other three pins are empty. There are three lead pins, the pin numbers 1, 4 is a power input terminal, pin number 6 is the power output terminal, pin numbers 1, 4 through the measuring input voltage is normal, the output pin 6 of the battery voltage. At this time, a problem, a circuit diagram can be seen, the pin 6 is controlled by the car lights, pin number 6 indicates an electric relay J317 pull, but only when the door or tailgate is opened when the interior lights will light now four doors and luggage compartment have been closedClosing, with a pin 6 12 V voltage is not normal.
Next, we checked the 6-pin plug T6k vehicle network control unit 3 in the plug, a circuit diagram of the analysis shows that the red T6k No. 6 pin plug pin 3 is connected to the luggage compartment lighting switch. When the tailgate is opened, the contact switch is closed luggage compartment lamp, No. 3 pin plug T6k turned on, the control unit recognizes the onboard network of the pin turned on after the relay control work J317, J317 pull, T6j plug pin No. 6 will have a 12 V power. Now all four doors and the tailgate are closed, is it that there is a short circuit to ground in places, causing relay J317 work?
and the wire harness is arranged to compare the vehicle specifications, a short circuit is unlikely. Therefore, I suspect a short circuit fault is caused by man (the installation of electrical appliances). Asking the user to know the car had only the installation of reversing radar, but uncontrolled car parking sensor and a network control unit, it can be ruled out.
While maintenance stalemate, I suddenly thought of one thing: The car sales and soon, users did not take long for this failure occurs, it may be added at the factory what electrical equipment, the user himself unclear. So I sold the car to ask the sales consultants, that this new car models are fitted with GPS vehicle anti-theft devices, failure is likely to be related to the GPS anti-theft device. I removed the GPS anti-theft device, the discharge current rapidly falls to really 0.02 A. So, GPS anti-theft devices and on-board network control unit have any link? I inspection line connecting GPS antitheft device and found that a wire connecting the control unit to the onboard network T6K No. 3 pin plug. The signal line pins luggage compartment is illuminated switch, due to internal GPS anti-theft device results in failure of the signal line is grounded, the network control unit onboard the deck lid that is opened, and the control relay J317 pull luggage compartment lights.
FIG 1
Solution: Replace the GPS anti-theft device (FIG. 1), failure to completely eliminate.
(Caoshou Jun)