K-line Issues with Aftermarket Radio (B5)

[down_n_dapper]

I'm trying to connect VCDS to my ECU which seems an impossible task. Without the radio on I can connect to the ecu with the ignition on, however running the engine I cannot connect.

I disconnected the stereo all together, nothing plugged into the wiring harness whatsoever and I still have 10.46V on pin 7 of the diagnostic connector and reader still cannot communicate which according to the vcds website means there is some sort of incorrect wiring in my aftermarket stereo. I tried to track down the k-line wire on my radio harness lastnight but was unable to find it.

Why would there be 10.46V on this K-line if nothing is connected to it and how do I find the k-line wire in the radio harness?

[CoyneJ]

Try unplugging abs under the hood

[down_n_dapper]

Try unplugging abs under the hood

I have tried this method in the past, before i got my abs repaired and it didn't help, however my abs now functions correctly and i am able to read every module except the ECU

[OldAudiA4]

Not sure if this will help but I remember when I was installing my aftermarket head unit into an early B5 A4, there was something slightly different about the wiring. http://www.audizine.com/forum/showth...-new-head-unit

[down_n_dapper]

Not sure if this will help but I remember when I was installing my aftermarket head unit into an early B5 A4, there was something slightly different about the wiring. http://www.audizine.com/forum/showth...-new-head-unit

appreciate the response! My headunit appears to be behaving, might've fluked the wiring right when I did it!

Did some digging around and decided to measure the K-line voltage from the diagnostic port under various conditions. Important to note this was across Pin 4 (chassis ground) and Pin 7 (K-line) with a good battery of standing 12.4v.

Being the B.eng student I am, excel works best to show results:


As I am able to scan the ECU with the ignition on, car not running, and fan on max where the voltage is 10.1v. I'm also confused there is still a voltage with the entire car off..

As for the radio, I've checked my wiring harness going to the headunit, there are no Kline wires going into it and its not mis-wired and the abs is clearly fine as shown in my testing.