Model: F02 with N52 engine.

Mileage: 104158Km

Fault phenomenon: the customer reported that the door lock of the main driving car could be closed but could not be opened, and the other three doors could not be opened or closed.

Fault diagnosis: see the fault phenomenon and empirically judge the power supply of central control lock, lock block fault or JBE fault.

Vehicle test has fault code:

·80209B central control lock: remove the damage of the chain relay or the fuse break

·80209D central lock: if the chain relay is damaged or the fuse is broken, ABL will prompt you to check the power supply fuse F14 15A and F15 20A.

F14 fuses are found broken and F15 is normal.

After the replacement of F14, the central control lock function is normal.

Similar faults were encountered before. In order to determine which lock block was the fault, a 5A fuse was connected in series from JBE to the four door lock block and the motor control line of the oil box cover. Half a year later, the fuse of the right front door lock block blew out, indicating that the right front door lock or circuit had short-circuit fault.However, the method of series fuse is too cumbersome, so I gave the customer a quotation of 4 door lock blocks. Because the customer did not agree with the cost problem, we must let us determine which lock block problem.After analyzing the circuit diagram (as shown in figure 1), it was decided to determine the fault by measuring the current and resistance of the lock block.

Figure 1 door lock circuit

The deadlocked motor current can be determined by measuring the MZS line current.

By measuring the MER wire you can determine the total current when the lock is opened.

The current of the locked motor can be determined by measuring the MVR line.

From the current size, it is not only possible to determine which lock block fault, but also further determine which motor damage caused.

Test the MER line current of normal vehicles (as shown in figure 2) :

Figure 2 MER current

2.57 A biggest

Minimum 2.53 A

Normal vehicle test MVR line current (as shown in figure 3) :

Figure 3 MVR current

1.54 A biggest

Minimum 1.49 A

MER line for the right front door of the defective car (as shown in figure 4) :

Figure 4 MER current of the right front door

· maximum current 3.47a

· minimum current 3.41a

MVR line at the right front door of the defective car (as shown in figure 5) :

Figure 5 MVR current at the right front door

· maximum current 2.36a

· minimum current 2.13a

Through measured four door lock on the block MZS, killing, MVR line current, and finally found the right front door lock motor current is too high, more than the normal standard of current car, in the state of fault measuring just 3.7 Ω trouble truck locked motor resistance, the normal car around 10 Ω, so you can determine the right front door lock piece of locked inside the motor due to the internal coil short circuit or resistance is occasionally lead to high current and make the F14 blown fuse.

Replace right front door lock block for troubleshooting.

Fault summary: although it is an accidental fault, it can also be found that the aging of the lock block motor causes the current higher than the standard range after comparison with the normal car.It is impossible to determine the control relationship between F14 and F15 fuses and the lock block circuit from the circuit diagram, but from the phenomenon, F14 fuse damage leads to the left front door can be locked and cannot be unlocked, the other three doors can neither be opened nor locked;The F15 fuse is damaged, so the left front door can be unlocked but cannot be locked. The other three doors can work normally, but four doors have no deadlock function.