Directly connect the diesel fuel pump?

Hello, despite some searching and a request in another forum, I haven't been able to find an answer to the following question yet. Perhaps someone here has experience with this and can tell me which starter relay is used?

I want to bleed the high-pressure pump on my Audi A4 B9 TDI facelift (year 2023). After a rear-end collision, the pump's carrier was replaced, which introduced air into the lines.

As usual, I tried using my VCDS: unfortunately, it no longer recognizes the vehicle - despite the supposedly lifetime software update. As an alternative, I could "simply" bypass the relay for the pump and let it run for a few minutes. However, my searches so far haven't yielded anything on this topic. I also don't have a wiring diagram yet.

Can anyone tell me where it's located and what the pin configuration is? Or if I can directly power it from a fuse somewhere? Using the relay would be a quick and easy solution for everyone who needs to fill their HD pump. I'm assuming that the pump is controlled by a relay, or possibly by triacs?


Thank you very much.

There are indications online that even with a USB-HEX version, most functions could potentially be accessed if Ross-Tech had released a software update for it. However, this is likely not the case. Too bad...

Hello Andreas,

I completely understand your frustration with the old HEX-USB+CAN interface. Let me look into the technical details and offer you a solution.

Why your interface (manufactured in 2015) does not support modern vehicles:
- Hardware limitation: Your interface has limited flash memory. New protocols and features (e.g., for VW Golf 8/ID models) require more space than is available for firmware on the interface. Software updates cannot help with this; only a corresponding interface hardware upgrade will solve the problem.
- "USB-HEX": This interface does not exist - you have the HEX-USB+CAN.

As a first-time owner of the HEX-USB+CAN , you are eligible for a discount when upgrading to:
- HEX-V2 (USB)
- HEX-NET (USB + Wi-Fi, including mobile diagnostics via browser).

With the current VCDS interface, the pump should be directly activatable via the actuator test function, eliminating any risk associated with makeshift relay solutions!

With HEX-V2/HEX-NET, you would:
1. In [Actuator diagnostics], proceed as follows:
2. Run the pump.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

→ Clean, secure, and documented!

Upgrade here:


Best regards, Rainer.

PS: The "Free Gift Box" promotion in 2015 was a bonus for you – the hardware itself was never designed for eternal compatibility. New technology always requires new hardware.https://shop.dieselschrauber.org/en/vcds-interface-upgrade-p-342.php

"I initially solved the problem in a different way: I disconnected the suction hose from the high-pressure pump, filled the pump and hose with diesel using a syringe, loosened the line leading to the furthest injector (but didn't disconnect it completely; this prevents back pressure). Then, I just cranked the engine for a few revolutions using the starter, tightened the line, and it started right up."