Peter Badore

After re-reading the posts about Audi symphony radio communication problems I installed a known good Concert radio in the flood 99 A6 Avant. Now using the VCDS option test the K1 line reports OK . However,
now there is no communication with any control module and/or device. Could a pulled, cut or open K line betwwen the OBD2 plug pin no. 7 and connection A76 in the I/P wiring harness cause this? I assume yes?
Also, does each individual control module separately provide battery + (at reduced voltage) to the K line OBD2 pin no.7?

Uwe@Ross-Tech.com

Yes, an open K-line could cause that.

Each device on the K-line is supposed to use an Open Collector type drive ciruit. It is the job of the scan-tool to provide the pull-up resistor to keep the K-line high when nobody is pulling it low.

-Uwe-

Peter Badore

VCDS still can't communicate with any control module or device. The OBD2 port pin no. 7 has continuity to
the K line pin on the black radio harness connector. All modules have been disconnected except for the last one being tested. The VCDS port test now always says K1 OK, K2 OK and CAN not ready. My question this time is what does the the VCDS port test actually check when the K1 line is reported as OK? And
could any K line wire shorted to ground prevent all the modules from communicating to VCDS?

Uwe@Ross-Tech.com

It tests that it can swing the K-line to +12 qnd GND (or more properly, at least to both logic levels). However, it does this test at a relatively low frequency, so excessive capacitance could produce an "OK" on this test where no communications is possible, as could an open circuit somehere between the pin on the IC where we actually look at this (inside the interface) and the K-line pin on the module in question.

Got an oscilloscope or a scope-meter?

-Uwe-

Peter Badore

No scope. I haven't needed one until now.

Theresias

No, but an aftermarket radio which replaced the Symphony might.

http://www.ross-tech.com/vag-com/aftermarket-radio.html