Shown below is the configuration schematics of 2007-2009 VW data bus network diagram for the DLC connector. To test NO COMMUNICATION fault message from your scanner, you can trace this bus wires coming from the DLC pin terminals. Using a digital voltmeter, you can check the voltages shown in the DLC pin terminals to verify the high and low speed network signals.
2007-2009 Data Bus Network Description:
Starting at the 16 pin terminals of the DLC on top, there are basically 3 terminal pins to check for bus communication:
PIN 6 which is the CAN Hi speed bus communication signal. When you measure it it with a voltmeter using PIN 5 as your ground, you should get 2.5 volts at key on engine off (KOEO). Take note that this voltage reading actually fluctuates between 2.5 volts to 3.5 volts at KOEO.
PIN 7 which is the K Line bus communication signal. This is a low speed bus signal and usually is a lone wire going to the accessory modules like Climatronic Control Module and the Radio as shown on top left. When testing for voltage, probe PIN 7 against PIN 5 and you should get about 7 volts st KOEO. If out of range, disconnect the 2 accessory modules one at a time along with TCM, Memory Seat module and Comfort System module.
PIN 14 is the High Lo bus communication signal. This bus is paired together with the CAN Hi bus wires which are twisted together. To measure the voltage of this bus at PIN 14, probe this pin against PIN 5 and you should get 2.5 volts average reading at KOEO. This voltage is also fluctuating between 1.5 volts to 2.5 volts.
Take note that that just below the 16 pin DLC terminals, we have the 20 connector data bus interface box where most data bus signals are coming from. Unlike the 2003 models, our DLC pin 6 now goes to connector 19 and DLC pin 14 goes to connector 9. These 2 high speed CAN bus wires are then fed to each of the modules thru their links (3 links shown here which is similar to the splice bars in GM). The only exception is the PIN 7 K Line bus signal which fed directly to the ECU at the bottom left.
Troubleshooting 2003 VW data bus network:
The only thing to watch is the resistance between the 2 high speed buses coming out at this Interface box. Example, if we measure the resistance at connector #6 and #16, we can isolate all the modules connected at Link 2.
I would still verify the ECU or DFI by going straight to the sensor like TPS or crank sensor to check for presence of 5 volt VREF. Make sure to verify all terminal connection fits for loose connection which can cause lost of communication.
NOTES on VW Bus Networks:
1.) The actual bus network diagram will show you the exact colors of the bus wires and locations of the modules in the circuit.
2.) This DLC diagram can be used for 2007-2009 VW models. The only difference is the number of modules being used on later models (it has more modules applied). Still, the Data Bus On Board Diagnostic Interface is use all the time as a gateway module.
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