Control units not responding, Audi A6 2.5 TDI (solved)

Hello,
It's about my Audi A6 Avant C4 2.5L TDI (AEL), manufactured in July 1997.

Recently, a series of beeps have been sounding during startup, and the red indicator light (!) is flashing continuously.

Unfortunately, I am unable to read the error codes.

I am using the HEX-V2 Dual-K & CAN USB interface (H12-047488) with an adapter cable to connect to a 4-pin connector (since the Audi does not yet have an ISO connector). The software is updated to the latest version.

The interface works great in our Golf 7.
I tested the four pins on the adapter connector and they show continuity.

VCDS detects the interface during the connection test, but not the lines K1/K2 (see screenshots).

"The reading failed; the control units are not responding."

Two weeks ago, I was still able to read error codes from the vehicle, but today, suddenly, nothing appears anymore. Otherwise, the car is running normally, except for the beeping and flashing lights.

What did I forget to mention?
What additional information might be needed to find a solution?
I don't know what to do next.

Thank you.

Benny.

Are there 12V present at the diagnostic connector? VCDS is reporting 0V there. (I have no idea if this could be the cause, I just noticed it.)

The +12V on one of the double connectors are necessary.

Hello,
Thank you for your input!

12V is present. The ground connection within the connector (pins 4 and 5) is established.

I've temporarily added something for testing purposes.
- The starter battery was disconnected for more than 10 seconds.
- used a different USB port.
- Used a different USB cable.
(The last two points are just out of desperation; the interface works perfectly with this notebook in my Golf.)

Hello,

Please take a voltage measurement with a load connected (using a test lamp).
You can also try taking the measurement with the interface connected and measuring the voltage at the 2x2 connector on the back.

VG
Thilo.

Does this interface work with a Golf that has a connector with two rows of two pins (2x2)?

Rüdi wrote:

Funktioniert das Interface an einem Golf mit 2x2 Stecker?

No, it's a standard ISO connector.

klahaui wrote:

Please take a voltage measurement with the load connected (test lamp). You can also try taking the measurement with the interface connected and measuring the voltage at the 2x2 connector on the back.

The measuring device shows approximately 12V whether the test lamp is connected or the diagnostic connector is plugged in.

The K-Line also provides 12V when the system is in standby mode. Please do not confuse the two connectors and under no circumstances connect them with reversed polarity!

Plug in your OBD2 adapter and take measurements at the OBD2 connector.
https://www.obd.wiki/obd-2-buchse

Best regards, Rainer.

Located on the K line.
approximately 9.4V when "ignition is on".
"With the engine running, approximately 10.8V."

Could the starter battery be too weak? The car hasn't been driven much lately, but the battery is only one year old. (I'll charge it just in case.)

Hello,
I had the battery on the charger over the weekend. The problem still persists.

However, today I tried to measure the voltage on the K-line again while having a test lamp connected, and the test lamp did not light up!

Voltage without test lamp connected (engine off): 10.0V. When I connected the test lamp at the same time, the voltage dropped to 0.04V.
The inspection lamp on the K-line is not lit today either.

benschke wrote:

Voltage without test lamp connected (engine off): 10.0V. When I connected the test lamp at the same time, the voltage dropped to 0.04V.

The behavior is normal; this is how the communication works. The bus participants pull the line to ground.

It would be important to check if the adapter receives the +12V power supply voltage and also has a ground connection at the OBD2 connector.

dieselschrauber wrote:

Wichtig wäre, ob am OBD2 Stecker vom Adapter die +12V Betriebsspannung ankommen und auch die Masse Kontakt hat.

With the adapter connected, there is a ground connection on both pins, as well as 12V on the positive terminal and 10V on the K-line. (Are the 10V correct, or should it be 12V?)

"Most likely, the 10V reading is acceptable, but it depends on what was used for measurement and how the voltage was loaded, as well as the internal circuitry within the control unit."

You would need to select a random K-Line transceiver and consult its datasheet.

What is definitely not okay is the lack of a 12V power supply for the diagnostic cable. Hopefully, the ignition is always on when using it?

dieselschrauber wrote:

What is definitely not okay is the missing 12V operating voltage for the diagnostic cable. Hopefully, the ignition is always on in this case?

Something's gone wrong.
The diagnostic cable is receiving 12V (as shown in the Screenshot above), and the ignition was also turned on in each case.

Hi there,
Perhaps I'm asking a silly question, but which specific red light is blinking continuously? The engine check light would be yellow.
Perhaps you could have a compatibility check done at Audi or Bosch?
hg
Herbert.