Failure phenomenon: a 2010 Audi A6L 2.8 L FSI sedan, mileage 1 065 km. Users reflect the car’s navigation 3G (third generation) does not work well in the running of the vehicle, MMI (Multi Media Interface) vehicles on the MMI screen cursor stagnation (Figure 1), other features on navigation systems (such as maps, path and other settings) were normal.
FIG 1
Analysis Check: After I pick, first fault diagnostic connector VAS5052A The system address code 5F, found no fault code memory. Taking into account the shielding effect of the building and there is signal interference in the maintenance shop, the synchronization can lead to not receive GPS satellite signals, so the author and the owner of the vehicle along a road test. In the road test, I found that no matter what position the car to travel, do not move the cursor. The problem of vehicle maintenance technician or a new challenge, due to the lack of experience in this regard troubleshooting, I sometimes do not know how to start.
MMI Navigation plus vehicle is equipped with an advanced version of the navigation system, a hard disk, an information electronic device control unit J794 front portion of the original information control unit J523, single-disc DVD drive, a navigation system control unit J401, telephone transceiver R36, voice input control unit and an external audio control unit J507 R199 (Audi music interface) highly integrated, wherein J794 MOST is to control the communication device on the bus (fiber), the operating system reads information from the multimedia unit E380, control and diagnostics for displaying MMI display J685, J533 and the interface MMI display instrument cluster J285 diagnostic data via the communication bus.
FIG. 2
According to the circuit diagram (FIG. 2), the electronic device I examination information and an antenna control unit J794 lines were normal. Press the button on the lower left corner of the navigation information MMI control panel, regardless of which direction the vehicle is traveling, GPS synchronous satellite on the MMI display, the displayed number of pieces is always 0, no change, it appears that the vehicle did not always receive the satellite signal, causing the vehicle navigation system can not locate. Because it is a new lessonQuestion, I dare to get involved, so the first analysis of positioning principle.
To pinpoint the vehicle navigation system to be received at least three satellite signals, the satellite transmits to the ground once every millisecond and the identification code and position precision time signal, the vehicle navigation system antenna amplifier for receiving satellite signals, the GPS RF signal converted into an intermediate frequency signal within the operating range of the signal processor, and the band suppresses the multipath interference, the SNR (signal noise ratio) to the level of the signal processor may work, and to provide a dynamic range of signal changes. Wherein the preamplifier (preamp) have a small noise figure, high gain and a large dynamic range of the amplifier, identifying each satellite signal separation by the signal processor module within the multiple access signals J794, the GPS spread spectrum signal is despread , demodulation carrier signal to noise ratio on the basis of the recovery, to eliminate the influence of the frequency offset, recover the baseband signal, and then despread correlation. Epoch demodulation processing corresponding to the code state and carrier phase state and form the original observations, together with the navigation data transmitted to the internal J794 application processing module, which provides real-time control of the signal processing module, for further processing and output calculate the vehicle position, speed, time and other information in order to meet the needs of the navigation system. Analysis of this point, I believe that there is no fault code information of the electronic device within the control unit J794, J794 is substantially no problem can be described, and the antenna line connection is normal, and therefore the problem is suspected in the antenna amplifier.
Figure 3
Troubleshooting: insulating windshield trim panel is removed after the author, found R50 antenna amplifier (FIG. 3) on the left, will replace it. At this time, the operation panel is pressed again MMI navigation information key immediately displayed on the MMI display four satellites, a car navigation function recovery, since the car navigation system is operating normally.
reviewed: By excluding car navigation failure, the author summed up an experience (for reference only): If you can not display the vehicle position on the MMI screen map, it means not receive GPS signals, the focus should check the antenna or antenna amplifier. Also new to this topic also inform you that car maintenance staff not only to fix the buried car, but also to learn new systems of automotive knowledge, understanding of the relevant principles of advanced vehicle systems. Only in this way, the maintenance staff to take on new challenges, so put someVector troubleshooting, efficiency will naturally increase.
(Lu Jianping)