Engine Control Unit Replacement: Immobilizer Active?

I need to replace the engine control unit (ECU) on my A4 (AFN) engine. Does it have an immobilizer?
Can it be activated? If so, can it be deactivated again using a tool like VAG-COM or similar?
The engine control unit (ECU) is a Bosch part with numbers 0281 001425/426, and the Audi part number is 028906 021.

Yes, it will then be active, but you can easily reset it because you have the Immo2 system. Simply log into the instrument cluster and set adjustment channel 10 to 0.

Regards,
Benjamin.

Possibly 'Channel 10' is a typo.

After replacing the engine control unit (ECU), the Wheel Speed Sensor (WFS) data needs to be adjusted to match the new ECU. This is also straightforward with Immo-2, but it's done in channel 00, not channel 10.

-Uwe-
VAG-COM Author.

I want to remove the existing control unit to find the connections for a one-button garage door opener. Is this something that can be done easily, or will I need to bypass any switches afterward?

Thank you, Edgar.

Hello,

When the ignition is off, the control unit doesn't receive any power anyway. Does that answer your question?

Best regards, Rainer.

Hello,

When the ignition is off, the control unit doesn't receive any power anyway. Does that answer your question?

Greetings, Rainer.

Not directly; I thought the same thing when disassembling the airbag seat, and even though the battery was disconnected, the interruption was still detected. This suggests that the airbag control unit was likely still receiving power for some time .

Specifically: Can anyone definitively tell me, based on their own experience, how the control unit behaves in this case?

Thank you, Edgar.

Again: Nothing is happening. This device simply CANNOT detect whether it's been removed or the battery has been disconnected.

That's not entirely correct. In modern cars (at least from the year 2000 onwards), engine control units always have two power supplies: one from terminal 15 and another from terminal 30. Therefore, turning off the ignition is not the same as disconnecting the battery or removing the control unit, because the control unit still receives power even when the ignition is turned off.

If you turn off the ignition, certain things that would normally only be updated in RAM are saved to the EEPROM in the control unit. Only after the control unit has done this does it truly go into sleep mode. Therefore, you should always turn off the ignition before disconnecting the battery or removing the control unit from the wiring harness. If both power sources disappear simultaneously, there is a possibility that your control unit attempts to update the EEPROM, but the current in the capacitors may not be sufficient, and this could result in data corruption within the EEPROM (checksum error). Such an error can be difficult to fix.

But back to the original question: There are no issues with the WFS if you remove and reinstall the same engine control unit, but be sure to turn off the ignition first.

-Uwe-

Learned something new again .

Hello,
Okay, since we're on the subject: How about the C4 TDI AEL engine? I plan to replace the engine control unit with a used one soon. Do I just need to plug it in, or are there any other things I should be aware of?
Regards,
Martin.

What is the manufacturing year of your C4? If the car has a Vehicle Security System (VSS), then the VSS needs to be adjusted with each control unit replacement. However, since it's definitely not an Immo-3 system, it's quite simple and doesn't require a PIN.

-Uwe-

Hello,
He was born in 1995. I think it's likely that he has an immobilizer system. How can I tell if he does?
What exactly do I need to do after the installation?
Regards,
Martin.

I also suspect that a '95 C4 has a WFS. You can tell if it does by using a diagnostic device (or software) and checking address 25, where the WFS should respond. Alternatively, you can try starting the engine with a key that is not programmed to the WFS, and it won't start.

After replacing the engine control unit, use a diagnostic tool (or software) and access address 25, function 10 (adaptation), channel 00, and enter a value of 0. Then, turn off the ignition, wait for 15 seconds, turn the ignition back on, and you're done. The engine should now start.

-Uwe-