Hello,

I've decided to swap my golf 4 ARZ ECU from 06A906032AR to 06A906032DR in order to keep my IMMO 2 but switch to a wideband lambda sensor.

To do this, I've used this plug and play harness: https://www.carrottoptuning.com/products/1-8t-vw-audi-wideband-conversion-harness-plug-n-play
And this Bosch lambda sensor 0258007351.

I've installed the harness (pins 52, 71, and 15), the lambda sensor, the ECU, everything seems fine.
I've performed the IMMO adaptation using VCDS: 17->Adaptation->00->Read->Save. The car starts.

Problem: As soon as i turn on the ignition, my fan starts running, then stops, then starts again, and so on.

The fan control seems to be out of control, and there are no errors reported with VCDS.

84€ for two connectors a bit of wire and a resistor with terminals? I'm getting too old for this shit...

For that amount of money I'd expect at least an answer to your question.

Here this is the wiring for the wideband, verify vs your existing.

I finally found the solution !

The problem was with ECU pins 41 and 61 as some have mentioned.
I wasn't sure because it didn't match the diagrams.

I tested by turning my air conditioning to the maximum, and the fan stopped.

So, I swapped pins 41 and 61, and the problem seems to be resolved. My fan now starts at 90°C on low and 96°C on high.