Symptom: Bora 1.8T, automatic transmission, luxury, idle speed when the pointer shaking, accompanied by hand brake light alarm, driving in normal.
    Fault diagnosis: first in the ignition state with V. A. G155l special diagnostic instrument detection channel 01 engine, channel 02 transmission, channel 17 instrument, channel 19 bus, no fault storage, only in the channel 03ABS system to detect "Enginecontrolunitreadfaultmemory / sp." Failure. Clear the fault after the start of the test and found that the speed when the speed indicator pointer in 10 ~ 30km / h up and down swing, while the hand brake light alarm (when the speed is greater than 15km / h, such as hand brake does not lift the alarm prompt). Observed tachometer also has a certain fluctuation, analysis may exist external electromagnetic interference, then cut off the xenon light booster and one by one plug the ignition coil experiment, the needle swings phenomenon does not disappear.
    Because of the trouble-free code storage, we mainly focus on troubleshooting points to solve the speedometer pointer in 20 ~ 30km / h swing failure. According to Bora 1.8T line maintenance experience, odometer through the T32 / 28 pin (connected to the green line 0.35) from the differential housing on the speed sensor (G22) signal, at the same time, through the instrument on the blue plug T32 / 3 The pin (connection blue / white line 0.35) transmits the vehicle speed signal to the J220 (engine control unit) for the relevant function control of the vehicle speed. Idle when the query engine data stream 0l-08-005 group 3 area, in the event of failure, the display is 20 ~ 30km / h; query instrument 17-08-002 group 1 area, in the event of failure, show 20 ~ 30km / h ; And query automatic 02-08-003 group l area always shows 0km / h. It is concluded that the instrument receives the vehicle speed sensor signal is wrong, while the wrong speed signal to the control unit.
    In view of this analysis, the instrument internal circuit processing system damage caused by the speedometer out of control is more likely. First replacement instrument (part number: lJD9208261.8T): the first step, the new instrument authorization 17-10-50- original car PIN - show the bottom of a plate to confirm, the second step, matching key 17-1l-PIN-10-2l - Number of keys. After replacing the instrument, start the car test, the speedometer is still idle at 20 ~ 30km / h swing.
    Disassemble the air cleaner assembly, unplug the G22 speedometer sensor three-hole plug, measure the harness connector 2 feet (connect white line), in the 15th ignition block when 10V, measuring harness connector 1 foot (connected black / White line), in the 15th ignition when the 0.5V, then analysis of the No. 2 foot should be G22 sensor 15 power supply line, 1 foot for the G22 signal line.
    Plug the G22, the use of pin method to lead the black / white line voltage signal, in the idle time to detect the output signal voltage is 0.5V, this time there have been idling speed indicator pointer up and down the situation of the vibration. Then the normal circumstances of its signal voltage is what value? Users then provide a message, the fault in the D block on the idle does not appear, so allow users to help hang D block idling, and sure enough the speed back to zero When the test black / white line output voltage of 13.8V.
    Speed ​​table normal display and abnormal display voltage will be so big difference, it is difficult to use the theory to explain, is it G22 signal distortion. Replace the G22, the fault still exists. G22 is driven by the plastic driven worm to produce magnetic flux, and drive the worm is driven by the ring on the differential housing; at idle, the differential case is stationary. Therefore, the G22 output should also be 0km / h, then from the mechanical failure analysis. It is impossible to cause G224 signal voltage distortion. At this point, the maintenance process into a deadlock. It was decided to directly cross the G22 signal line to the instrument T32 / 28 pin test. Before that, first find the circuit diagram to study carefully, see the G22 power supply line, it suddenly realized that the original G22 by the black / white line power supply, rather than white / blue line, after the measurement voltage of 0.5V, obviously that G22 The electrical circuit is open or too large.