Symptom:The customer said that every time the ignition is turned on, the wipers will automatically work once and then return to the original position.
Troubleshooting:According to the fault phenomenon described by the customer, after repeated test run, the author found that this situation will definitely occur at the moment when the ignition switch is turned on, and other functions of the wiper, whether in intermittent gear, first gear or second gear, are working normally.Use the VAS6150 to enter the body control module and check that there is no fault memory. What is the reason for this?Since the electronic detection system reflects that everything is normal, the fault can only be analyzed from its working principle, and then checked according to the relevant circuit.The components associated with the wiper system include the wiper motor, wiper relay, body control unit, gateway J533, steering column electronic control unit J527 and wiper switch. The simplified circuit is shown in Figure 1.
Figure 1 Wiper Control Circuit
The working process and control principle of a wiper motor can be seen through the circuit diagram, which is conducive to subsequent fault analysis and troubleshooting.First of all, the working principle of the wiper motor is essentially different from that of the ordinary wiper motor of the previous models. The former ordinary wiper motor is just a simple actuator, that is, an ordinary motor. It is connected with a ground wire, a low-speed power supply wire and a high-speed power supply wire. In addition, there is a normal hot wire for the automatic return of the wiper motor.As long as power is supplied to the power supply line of the corresponding gear, the motor will work.The wiper motor of this model is not only an actuator, but also an integrated wiper control unit (belonging to a sub control unit). The control unit is also connected with four lines, one control line (LIN line communicates with the on-board network control unit), the other is a ground wire, and the remaining two are directly connected to relay J369 (R1)On the two output terminals (No. 1 and No. 5).
Next, we will learn about the working process of a wiper motor. As can be seen from the figure, except for No. 3 (purple/white), which is LIN line, and No. 4 (brown), which is ground wire, only No. 1 (green/yellow) and No. 2 (green/black) lines are connected to the relay. These two lines are the power supply lines of the wiper control unit,Observe that the two relays J368 (R2 for short) and J369 (R1 for short) in the figure are connected in series with each other. R2 is connected in series at the front end and only terminal 5 is connected to the fuse (normal live wire). Therefore, terminal 5 is the only power line when the wiper operates, regardless of the gear of the wiper,R2 relay must be in working state to provide working power to the wiper control module, while R1 relay, regardless of whether it is working or not, always has one of its internal two contacts closed, so as to transmit the power supply of R2 relay to the wiper control unit through the contacts, so that the wiper motor can run at the corresponding speed.To facilitate understanding, the circuit direction of a wiper motor at each gear is simulated according to the circuit diagram below:
When the driver turns on the first gear switch of the wiper, the wiper switch will directly transmit the analog signal to J527, and J527 will transmit the signal to gateway J533 through CAN line, and then J533 will transmit the signal to the on-board network control unit J519 through CAN line,After receiving the first gear signal of the wiper, J519 provides the 52b/23 pin with a low potential signal, so the R2 relay coil is energized, and contacts 3 and 5 are connected. The power supply passes through the battery → fuse → R2 relay (pin 5 → contact → pin 3) → line to R1 relay (pin 2 → contact → pin 1) → pin 2 of the wiper control unit, so the wiper runs at the speed of first gear.At this time, R1 relay does not work, but its normally closed contact acts as a wire.
When the driver turns on the high gear switch of the wiper, the same way through the first gear,When J519 receives the command transmitted from J527 and needs to turn on the high gear of the wiper, it will provide 52b/18 and 52b/23 low potential signals at the same time, so R1 and R2 work at the same time. At this time, R1 relay contacts are pulled in, and the power supply passes through R2 relay contacts, then R1 relay (pin 2 → pin 5) → wiper control unit pin 1,At this time, the wiper motor is running at high speed.
Another working state of the wiper motor is intermittent gearPassatIn the vehicle model, the duration of wiper intermittent gear can be adjusted as a standard configuration, and its interval working time is 4s, 9s, 16s and 24s respectively. This signal is directly output by the on-board network control unit through LIN line to let the wiper control unit work.Of course, when the wiper operates in intermittent gear, the speed of the wiper motor works in gear 1. At this time, the power supply path and gear 1 working path are identical, but the interval time is controlled by J519.
According to the above analysis, combined with the fault phenomenon in this case, it is felt that the two wiper relays R1 and R2 should not have problems, because if either of the two relays has any fault, the wiper motor may not work normally.Then the next most likely part should be the control part, including the wiper control unit itself, or the J519 itself.
It is doubted that the electronic control unit itself has a fault, and it is the fastest way to replace it if conditions permit. However, the fault is still the same after the technician replaces the wiper control unit on the same type of vehicle according to this idea, while the wiper control unit on this vehicle is replaced by another vehicle, but no similar fault will occur, and then the on-board network control unit J519 is replaced,However, the fault phenomenon has not changed at all, which indicates that the judgment is wrong.So what's the problem?
Think about this strange phenomenon again and again. One operation of the wiper is equivalent to the intermittent gear opening of the wiper. Is it possible that there is a problem with the LIN line of the wiper control unit?With this idea, directly pick out the T4a/3 and T52b/20 pins of the wiper control unit and fly another wire. The fault still exists.This indicates that the assumption is still not tenable, and the maintenance has reached a deadlock.
As there are only a few accessories for wiper control, apart from two control units (on-board network control unit and wiper control unit), there are two relays R1 and R2. The relay itself is very simple, just an actuator, which only serves to transmit voltage signals. If there is no external control,It is absolutely impossible for a relay to work so regularly.So where is there any doubt?Could it be that the wiper switch itself gives an incorrect signal?If the wiper switch gives an incorrect signal, the J519 cannot read any fault code. However, if this assumption is correct, the error signal should not only be given at the moment of key opening.However, in order to eliminate this possibility, the author reads the data stream in J519, repeatedly turns on and turns off the wiper switch, and the signal displayed in the data stream conforms to the state of the switch. So far, it shows that the wiper switch is normal, and the problem is not related to the wiper switch.
Since there is no problem with the relevant components, the focus is still on checking the circuit.Since the wiper motor has been removed, it is also very convenient to measure the ground voltage of each pin of a wiper motor at the moment when the key is turned on and off.The measurements are as follows: when the ignition switch is turned off, T4a/1 (green/yellow) is 0V, T4a/2 (green/black) is 0V, T4a/3 (purple/white) is 12V, and T4a/4 (brown) grounding is normal.This measurement is within the normal operating range.Then measure the voltage between each pin and T4a/4 when the ignition switch is turned on. T4a/1 is 8V, T4a/2 is 12V, and T4a/3 is 12V.This test result obviously reflects that T4a/1 and T4a/2 have voltage at the moment when the ignition switch is turned on, which must be an abnormal condition. The direct result is that the wiper runs at a low speed once, which is consistent with the fault phenomenon in this case.It can be seen from the circuit diagram above that T4a/1 and T4a/2 are both connected to R1. Is there really a problem with the relay?To eliminate this problem, replace two new relays first, and then turn on the ignition switch. The fault still exists. So far, it indicates that the problem is in the control part of the relay. Next, check the circuit.In order to judge which line is faulty, find the same model and measure the data of relevant lines of the wiper control unit: when the wiper switch is turned off and the ignition switch is turned on, T4a/1 is 0V, T4a/2 is 0V, and T4a/3 is 12V;This result is obviously different from the fault vehicle. After turning on the ignition switch, the corresponding pin voltage of the wiper control unit and the working state of the relay are shown in the table.
Normal working data of wiper control module
Then measure the voltage data of each pin when the wiper control unit of the faulty vehicle is in each gear. After comparison, the data is completely normal. The abnormal data is that there is a sudden voltage at T4a/1 and T4a/2 at the moment of turning on the ignition switch. This is the root cause of the instantaneous operation of the wiper, and these two pins are from R1,However, the output voltage on R1 comes from R2. If R2 does not work, then there is no voltage on R1. Then the root cause of the problem should be R2. Therefore, the next step is to focus on the control part of R2.
According to this idea, recheck R2's own control circuit and related power supply circuit (including SB14 fuse). As shown in Figure 2, they are all concentrated on the SB fuse holder.
Figure 2 Fuse and Relay Locations
Since R2 and the fuse are inserted on the base, in order to remove the fault, the fuse base must be carefully removed. During the removal process, it was found that several pins at the bottom of the integrated base were almost coming out, and these pins were just connected to the 2 # pin of R2, so it was re inserted into the corresponding hole and fixed, and finally other parts were restored,It was found that the fault of the car was finally eliminated during the test run. So far, it can be determined that the fault of the car is caused by the fuse integrated seat (in theengineIt is caused by the looseness of the wire speed pin behind the front left).
Fault summary:Although the fault has been eliminated, it is necessary to continue to explain about the LIN line of the wiper. According to the author's test, when the LIN line is broken, the wiper will automatically run once when the ignition switch is turned on. This is exactly the same as the fault in this article. The difference is that the wiper will run again once the ignition switch is turned off.When LIN line is short circuited or grounded, the wiper will always work in intermittent gear, which is not controlled by the switch.This can be regarded as an emergency control of the wiper control unit.
The wiper control module also has several functions, including replacing the maintenance position of the wiper blade. Within 10s of turning off the ignition switch, push the wiper switch to the inching position, and the wiper will automatically stop to the highest position, so that the maintenance personnel can replace the wiper blade easily.There is also an APP function of the wiper. This function is that the wiper arm will move slightly upward after returning to the lowest position.Each time the wiper system is turned off twice, it works once.The APP function will automatically activate after every 100 cycles of wiper operation.The main function of this function is to prevent the wiper blade from being fixed at the same position every time, resulting in early aging of wiper blade contact.Finally, it also includesengineWhen the vehicle hood is opened, if the vehicle speed is lower than 16 km/h, the wiper is prohibited from working, but if the wiper switch is toggled again, the wiper is activated.When the vehicle speed is higher than 16km/h, although the hatch cover is not closed, the wiper will still work, and the wiper will not be disabled again until the vehicle speed is lower than 2km/h.
Brand Specialty: (Keyword:After Passat turns on the ignition switch, the wipers will work automatically once. Several car electrical appliances will be repaired)
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