Failure phenomenon
A FAW Audi Q3 6L SUV produced in 2010, equipped with CAD engine, has a mileage of 19,753km, and the owner reflects that the driver's seat is not ventilated properly.
Fault diagnosis and remove
1. Audi seat ventilation function is set by MMI, which belongs to comfortable CAN bus system. The accompanying car owner sets the driver's seat ventilation in MMI, and the ventilation is normal within 2 minutes. After that, it does not work and cannot be set again.
2. Use VAS5052 detection data bus diagnostic interface, address code 36 driver seat/steering column adjust control unit J136, store fault code: Driver seat back fan open circuit/open circuit to ground, static.
3. Select guiding fault query and select "final control diagnosis function" to drive the seat fan to work, and the driver seat back fan can work according to instructions for 10 seconds.
4. According to the driver's seat fan arrangement (figure 62) and circuit diagram (Figure 63), J136 receives the seat ventilation setting signal and divides it into two ways to supply power to the fan motor. The first way is seat cushion fan motor 1-V390, 2-V419, and the second way is seat back fan motor 1-V388, 2-v417. Two motors are connected in parallel each way, and each motor is connected to 3 wires, of which 2 are power lines and 1 is control signal lines.
5. According to the working principle, the reasons for the failure include: Driver seat back fan motor failure, related line failure and J136 failure. Because the "final control diagnosis function" can drive the backrest fan motor, it is considered that the possibility of fan motor and circuit failure is not large, and it may be that the seat ventilation cannot work normally due to false alarm caused by J136 failure.
6. After switching J136, the Test starts, the seat is normal, but after a while, the fault code is stored: the driver seat back fan is open circuit/open circuit to the ground, static. Indicates that the fault still exists.
7. According to the circuit diagram, measure the lines of the backrest fan motor V388 and v417. no abnormality is found. The resistance of fan motor V388 and V417 were measured respectively, all of which were 2Ω, and no abnormality was found. It is decided to replace V388 and V417 respectively. After replacing V388, the ventilation of the driver's seat will return to normal and the fault will be eliminated.
Failure point: driver seat back fan motor 1-V388 failure.
Maintenance summary
The seat ventilation function is an optional equipment for high-end cars. There is no abnormality in measuring the resistance of the backrest fan motor V388. Because it is a static measurement, whether the dynamic resistance is normal should be considered, but the dynamic resistance cannot be measured, therefore, the replacement method is adopted to finally find the fault point.
