EMU Black on VR6 BUB (TT 8J) – No permanent +12V, radiator fan runs on plug-in

[mihanic90]

Hi everyone,

I’m wiring an ECUMaster EMU Black to a VR6 BUB engine (Audi TT 8J platform) using the original OEM harness with a custom adapter (not PnP).

As a base, I used the BUB-pinout-spreadsheet-v2.pdf for the wiring.

I am also using the audia3_r32_bub_fw_3_057_v1.emub3 base map as a starting point.

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Current wiring setup:

• OEM pin 3 (Main Relay +12V)
  → connected to pin 13 (Battery +12V) on EMU Black

So the ECU does not have a permanent +12V, only supply via main relay.

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Symptom:

• As soon as I plug in the ECU connector (even without ignition ON),
  the radiator fan starts running immediately.

The car still uses the OEM fan control module (J293).

This happens before ignition and before ECU initialization.

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My questions:

1. How did you wire Battery +12V on EMU Black when using OEM BUB harness?

   • Did you run a separate permanent +12V from battery?

   • Or did anyone successfully use only main relay supply?

3. Does EMU Black require permanent +12V for proper initialization,
   even when using OEM wiring?

4. Has anyone experienced similar behavior:

   • fan running immediately after plugging ECU

   • outputs activating without ignition?

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Additional question (PnP version):

There is also a PnP version of EMU Black for VAG,

which plugs into the factory harness without adding extra wires.

• How is permanent +12V handled in that case?

• Is it internally sourced from the OEM harness (e.g. terminal 30)?

• Or is there still a constant supply present in the stock wiring that I might be missing?

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Additional observation:

In the BUB-pinout-spreadsheet-v2.pdf there is no mention of pin 62 (0.5 mm², permanent +12V / terminal 30) from the OEM ECU connector.

However, in the factory wiring this pin is present and supplied from fuse SC36, shared with the main relay (J271).

Could this be the correct source for permanent +12V for EMU Black?

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From my understanding, this could be related to:

• missing permanent +12V

• or backfeeding / floating outputs through the fan control module

I’d really appreciate any real-world wiring examples or diagrams from BUB setups.

Thanks!

[mihanic90]

Problem solved.

I am using a universal ECUMaster EMU Black (not the dedicated BUB PnP version) with a custom adapter built using the ECUMaster wiring documentation.

The issue was caused by combining the OEM Main Relay control and Fuel Pump Relay control into the same AUX output. I did not consider that the relay coils could feed back into each other through the OEM wiring and fuse distribution, which caused phantom power/backfeeding issues, radiator fan activation, and partial module wake-up even without ignition.

This could probably be isolated with diodes, but I decided to separate them properly instead:
• Main Relay → dedicated AUX
• Fuel Pump Relay → dedicated AUX

I actually prefer this solution because the Fuel Pump output has the normal 2-second prime behavior at ignition ON, while I wanted the Main Relay output to stay independent and stable.

After separating the relay controls, everything works correctly.